Variable optical-property element

ABSTRACT

An optical apparatus includes a variable optical-property element to change its optical properties by applying an electric or magnetic field or temperature to a liquid crystal. In this way, the optical apparatus is reduced in thickness, and can be used in a camera, a microscope, etc.

CROSS REFRENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.09/344,490, filed Jun. 25, 1999 now U.S. Pat. No. 6,437,925, the entirecontents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This Invention relates to an optical apparatus including an imagingdevice using an extended surface optical element and a variableoptical-property reflecting mirror, or including a variableoptical-property element, a variable optical-property mirror, or acombination of the variable optical-property element with the variableoptical-property mirror.

2. Description of Related Art

For a conventional, variable optical-property element such as a variablefocal-length lens or a variable focal-length lens, a description will begiven of the variable focal-length lens as an example. In an opticalsystem, an extended surface optical element may be used. The extendedsurface of the extended surface optical element refers to any surfacewhich has a shape such as a spherical, planar, or rotational symmetricalaspherical surface; a spherical, planar, or rotational symmetricalaspherical surface which is decentered with respect to the optical axis;an aspherical surface with symmetrical surfaces; an aspherical surfacewith only one symmetrical surface; an aspherical surface with nosymmetrical surface; a free-formed surface; a surface with anondifferentiable point or line; etc. In optical systems having usedoptical elements with the extended surfaces, an optical system utilizingthe reflection of the extended surface has the merit that chromaticaberration is not produced. This optical system, however, has thedisadvantage that in the case where the shape of the extended surface isabnormal, when the optical element is moved for zooming and focusingoperations, a mechanical structure such as a moving mechanism becomescomplicated.

A conventional digital camera, as shown in FIG. 1, has been manufacturedby assembling components such as plastic lenses PL, a stop D, a solenoidFS for focusing, a shutter S, a charge-coupled solid-state image sensorCCD, a signal processing circuit PC, and a memory M. Consequently, thenumber of parts is increased and an assembly becomes troublesome. Thus,there are limits to a compact design, accuracy improvement, and costreduction of the camera.

Furthermore, in general, the plastic lens has a tendency that itsrefractive index and shape change with temperature and humidity, andthus imaging performance is degraded by temperature change. In this way,glass lenses are chiefly used, and a lightweight design, accuracyimprovement, and cost reduction of the camera are highly limited.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to providean optical system including an optical element with a extended surfaceand a variable optical-property reflecting mirror.

It is another object of the present invention to provide an imagingdevice having the above optical system and an image sensor.

It is still another object of the present invention to provide anobserving device or an optical finder having the above optical systemand a display element.

It is a further object of the present invention to provide an opticalapparatus including an electronic imaging system and an electronicdisplay system, used in a digital camera, an electronic endoscope, a PDA(personal digital assistant), a video telephone, a VTR camera, or a TVcamera, which is capable of achieving a compact design and costreduction by integrally constructing parts such as an image sensor andan optical element through the technique, for example, of lithography,or including a platelike unit constituting a part of the above elements.

It is a still further object of the present invention to provide anoptical apparatus capable of compensating for a change of imaging oroptical performance by temperature and humidity, for example, a digitalcamera, an electronic endoscope, a PDA, a video telephone, a VTR camera,a TV camera, a film camera, a microscope, a laser scanning microscope, abar-code scanner, a bar-code reader, or a pick-up device for opticaldisks.

The optical system of the present invention includes extended surfacesand a variable optical-property reflecting mirror.

The imaging device of the present invention is provided with an opticalelement having extended surfaces, a variable optical-property reflectingmirror, and an image sensor so that the reflecting mirror and the imagesensor are placed on the same substrate, and the whole or a part of thereflecting mirror and the optical element having the extended surfacesconstitutes an optical system.

The imaging device of the present invention is provided with an opticalelement having extended surfaces and a variable optical-propertyreflecting mirror so that the reflecting mirror is placed close to onesurface of the optical element.

The optical apparatus of the present invention is such that a ray oflight following the direction of image formation or observation has ahelical relationship with a ray of light entering an image sensor or theeye.

The optical apparatus of the resent invention is provided with anextended surface prism in which a ray of light incident on the extendedsurface prism has a helical relationship with a ray of light emergingfrom the extended surface prism.

The optical apparatus of the present invention has a moving opticalelement comprised of an optical element and an actuator, including alithography process in a fabrication process.

The optical apparatus of the present invention has at least one of anoptical element, a shutter, a stop, and a display element, and an imagesensor on a single substrate.

The optical apparatus of the present invention has at least two of anoptical element, a shutter, a stop, a display element, and an imagesensor on a single substrate.

The optical apparatus of the present invention has at least one of animage sensor, an optical element, a shutter, and a stop, and a displayelement on a single substrate.

The optical apparatus of the present invention includes a variableoptical-property element.

The optical apparatus of the present invention includes a variableoptical-property mirror. According to the present invention, thevariable optical-property mirror is comprised of a combination of avariable optical-property lens with a mirror.

These and other objects as well as the features and advantages of thepresent invention will become apparent from the following detaileddescription of the preferred embodiments when taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the construction of a conventional digitalcamera;

FIG. 2 is a view showing an optical system using a liquid crystal inwhich the anisotropy of refractive index is negative;

FIG. 3 is a view showing the index ellipsoid of the liquid crystal ofFIG. 2;

FIG. 4 is a view showing a state where an electric field is applied tothe liquid crystal of FIG. 2;

FIG. 5 is a view showing a state of the orientation of liquid crystalmolecules;

FIG. 6 is a view showing another state of the orientation of the liquidcrystal molecules;

FIG. 7 is a view showing a pattern formed on an orientation film;

FIG. 8 is a view showing another pattern formed on the orientation film;

FIG. 9 is a view showing a liquid crystal lens in which the orientationof the molecules of a liquid crystal is changed with a high speed;

FIG. 10 is a view showing a state where an electric field is applied tothe liquid crystal of FIG. 9;

FIG. 11 is a view showing the liquid crystal lens looking at along thedirection of a z axis in FIG. 10;

FIGS. 12A and 12B are views showing a modification example of the liquidcrystal lens of FIG. 9 looking at along the directions of z and x axes,respectively;

FIG. 13 is a view showing an imaging device using the liquid crystallens of the present invention;

FIG. 14 is a view showing the liquid crystal lens looking at along thedirection of the z axis in FIG. 13;

FIG. 15 is a view showing a variable focal-length optical system usingthe variable optical-property element of the present invention;

FIG. 16 is a view showing an imaging device provided with zoom lensesusing the liquid crystal lenses of the present invention;

FIG. 17 is a view showing a liquid crystal lens using a polymer;

FIG. 18 is a view showing a state where an electric field is applied tothe liquid crystal of FIG. 17;

FIG. 19 is a view showing a liquid crystal lens provided with a heater;

FIG. 20 is a view showing a change of the orientation of liquid crystalmolecules caused by heating of the heater in FIG. 19;

FIG. 21 is a view showing an example in which the orientation of liquidcrystal molecules is changed by a magnetic field;

FIG. 22 is a diagram showing an electronic circuit for correcting animage derived from the imaging device of the present invention;

FIG. 23 is a view showing an imaging device using a variablefocal-length mirror;

FIG. 24 is a view showing one modification example of the mirror of FIG.23;

FIG. 25 is a view showing another modification example of the mirror;

FIG. 26 is a view showing variable focal-length spectacles;

FIG. 27 is a front perspective view showing an electronic camera inwhich the variable optical-property element of the present invention isincorporated in a finder optical system;

FIG. 28 is a rear perspective view showing the electronic camera of FIG.27;

FIG. 29 is a view showing the interior arrangement of an electroniccamera to which the present invention is applied;

FIG. 30 is a view showing one modification example of the embodiment ofFIG. 29;

FIG. 31 is a view showing another modification example of the embodimentof FIG. 29;

FIG. 32A is a view showing the entire system of an electronic endoscopeapparatus in which the variable optical-property element of the presentinvention is incorporated in an objective optical system forobservation;

FIG. 32B is a view showing the interior arrangement of the distal end ofthe endoscope of FIG. 32A in which the variable optical-property elementof the present invention is incorporated;

FIGS. 33, 34, and 35 are views showing examples of decentered prismsapplicable in the present invention;

FIG. 36 is a view showing an image display device using variableoptical-property elements in the present invention;

FIG. 37 is a sectional view showing the image display device of FIG. 36;

FIG. 38 is a view showing one embodiment of the optical apparatus of thepresent invention;

FIG. 39 is a view showing another embodiment of the optical apparatus ofthe present invention;

FIG. 40 is an enlarged top view showing a microshutter and itsvicinities in the optical apparatus of FIG. 39;

FIG. 41 is a view showing a modification example of a stop used in theoptical apparatus of the present invention;

FIG. 42 is a view showing a further embodiment of the optical apparatusof the present invention;

FIG. 43 is a perspective view showing a low-pass filter used in theoptical apparatus of FIG. 42;

FIGS. 44, 45, and 46 are views showing other embodiments of the presentinvention;

FIG. 47 is a view showing one modification example of the embodiment ofFIG. 46;

FIG. 48 is a view showing another modification example;

FIG. 49 is a view showing a modification example of the embodiment ofFIG. 48;

FIGS. 50 and 51 are views showing other embodiments of the presentinvention;

FIG. 52 is a view showing one example of the configuration of electrodesused in a variable optical-property mirror in FIG. 51;

FIG. 53 is a view showing another example of the configuration of theelectrodes in FIG. 51;

FIGS. 54, 55, 56, and 57 are views showing other embodiments of thevariable optical-property mirror of FIG. 51;

FIG. 58 is a plan view showing an example of a thin-film coil used inthe variable optical-property mirror of FIG. 57;

FIG. 59 is a view showing a modification example of the variableoptical-property mirror of FIG. 57;

FIG. 60 is a view showing another embodiment of the variableoptical-property mirror;

FIG. 61 is a plan view showing one example of an array of coils used inthe variable optical-property mirror of FIG. 60;

FIG. 62 is a plan view showing another example of the array of coils;

FIG. 63 is a plan view showing an array of permanent magnets suitablefor the array of coils of FIG. 62;

FIG. 64 is a view showing an example of an optical apparatus using areflecting mirror with an extended surface in the present invention;

FIG. 65 is a view showing an example of an optical apparatus using aplurality of variable optical-property mirrors in the present invention;

FIG. 66 is a view showing another embodiment of the present invention;

FIG. 67 is a view showing an electrostatic lens used as a moving lens Inthe present invention;

FIG. 68 is a view showing another embodiment of the present invention;

FIG. 69 is a view showing schematically a self-running lens used in theembodiment of FIG. 68;

FIG. 70 is a view showing another embodiment of the present invention;

FIG. 71 is a plan view showing an extended surface prism used in theembodiment of FIG. 70;

FIG. 72 is a side view showing the extended surface prism in FIG. 70,looking at from the object side;

FIG. 73 is a view showing another embodiment of the present invention;

FIG. 74 is a view showing an example of a conventional imaging device;

FIGS. 75 and 76 are views showing other embodiments of the presentinvention;

FIG. 77 is a sectional view showing a finder section of the embodimentof FIG. 76;

FIG. 78 is a view showing another embodiment of the present invention;

FIG. 79 is a view showing an optical element used in the embodiment ofFIG. 78;

FIG. 80 is a view showing the orientation of liquid crystal moleculeswhere a voltage is applied in FIG. 79;

FIG. 81 is a view showing one modification example of the opticalelement of FIG. 79;

FIG. 82 is a view showing another modification example of the opticalelement;

FIG. 83 is a view showing another embodiment of the present invention;

FIG. 84 is a view showing a variable focal-length Fresnel mirror used inthe embodiment of FIG. 83; and

FIG. 85 is a view showing an application example of a variablefocal-length diffraction optical element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before undertaking the description of the embodiments, it will beexpedient to explain the definitions of terms employed in the presentinvention. An optical apparatus used in the present invention refers toan apparatus including an optical system or optical elements, or a partof this apparatus. The optical apparatus need not necessarily functionby itself. That is, it is may be thought of as a part of an apparatus ora unit.

The optical apparatus includes an imaging device, an observation device,a display device, an illumination device, and a signal processingdevice. The imaging device refers to, for example, a film camera, adigital camera, a TV camera, a VTR camera, or an electronic endoscope.The observation device refers to, for example, a microscope, atelescope, spectacles, binoculars, a magnifier, a fiber scope, or afinder. The display device includes, for example, a liquid crystaldisplay, a viewfinder, a head mounted display, or a PDA. Theillumination device includes, for example, a stroboscopic lamp forcameras, a headlight for cars, a light source for endoscopes, or a lightsource for microscopes, Finally, the signal processing device refers to,for example, a read/writ device for optical disks, a bar-code reader, abar-code scanner, or a computer for optical calculators.

The variable optical-property element can be used in the opticalapparatus, and its compact and lightweight design and functionimprovement are achieved.

An extended surface can be defined as follows: Any surface issatisfactory which has a shape such as a spherical, planar, orrotational symmetrical aspherical surface; a spherical, planar, orrotational symmetrical aspherical surface which is decentered withrespect to the optical axis; an aspherical surface with symmetricalsurfaces; an aspherical surface with only one symmetrical surface; anaspherical surface with no symmetrical surface; a free-formed surface; asurface with a nondifferentiable point or line; etc. Moreover, anysurface which has some effect on light, such as a reflecting orrefracting surface, is satisfactory. In general, such a surface ishereinafter referred to as the extended surface.

An extended surface optical element refers to an optical element such asa prism, reflecting mirror, or lens which has at least one extendedsurface. Each of an extended surface prism and an extended surfacereflecting mirror is constructed with one optical block.

A variable focal-length lens used as the variable optical-propertyelement of the present invention has a structure shown in FIG. 2, forinstance. In this figure, reference numeral 1 represents a liquidcrystal in which the anisotropy of refractive index is negative, 2represents orientation films, and 3 represents transparent electrodeswhich are provided on transparent substrates 4 and 5, respectively.

In the optical element thus constructed, the liquid crystal 1 in whichthe anisotropy of refractive index is negative has the shape of an indexellipsoid such as that shown in FIG. 3, and satisfies the followingconditions:

ne<n_(ox), ne<n_(oy)  (1)

where ne is a refractive index of an extraordinary ray, n_(ox) is arefractive index of polarized light in the x direction, and n_(oy) is arefractive index of polarized light in the y direction.

The liquid crystal 1 also satisfies the following condition:

n_(ox)=n_(oy)≡n₀  (2)

where n₀ is a refractive index of an ordinary ray.

In such a variable focal-length optical element including the liquidcrystal in which the anisotropy of refractive index is negative, theorientation films 3 are constructed so that when the voltage is notapplied to the liquid crystal 1, the molecules of the liquid crystal 1in the z direction are oriented in the direction of an optical axis 6,that is, in a Z direction. Also, the orientation film 3 may be removed.In this case, the refractive index of the liquid crystal relative to theincident light is n₀, and the optical element functions as a positivelens.

In FIG. 2, when a switch 9 is turned on through an AC power supply 8,the orientation of liquid crystal molecules 10 is shifted as shown inFIG. 4 and thus a refractive index n relative to the incident light islowered as expressed by the following equation:

n=(ne+n ₀)/2  (3)

Due to such a reduction of the refractive index, the optical elementdiminishes its refracting power as the positive lens to increase thefocal length, and behaves as the variable focal-length lens. Moreover,the resistance of a variable resistor 13 is changed, and thereby therefractive index is continuously changed. Consequently, the focal lengthof the optical element can be continuously changed.

The orientation films 2 are prepared so that the liquid crystalmolecules 10 are oriented in a vertical direction, and as shown in FIG.5, orientation angles A of the liquid crystal molecules 10 become randomin an x-y plane. Therefore, even through any polarized light is incidenton the optical element, the optical element acts as the variablefocal-length which has the same focal length. Also, the liquid crystal 1has an original nature that produces a homeotropic orientation such asthat shown in FIG. 1, and thus the orientation films 2 need notnecessarily be used. In order to change the orientation of the liquidcrystal molecules 10, the frequency of the electric field, the magneticfield or the temperature, instead of the voltage, may be changed.

Even when the liquid crystal molecules 10, as shown in FIG. 6, areregularly oriented nearly perpendicular to one another, the same effectas in FIG. 5 is secured. In this case, it is desirable that a period Sof the orientation of the liquid crystal molecules 10 is less than thewavelength λ of light used, so as to satisfy the following condition:

0.5 nm<S<λ  (4)

This is because the scattering of light is minimized and flare isreduced.

Here, the wavelength λ is in the range of 350-700 nm for visible light.That is, in the case of the visible light, the condition of the period Sis as follows:

0.5 nm<S<700 nm

In the case of near-infrared light, the wavelength λ is in the range of650-1200 nm, and thus Condition (4) can be expressed as follows:

0.5 nm<S<1200 nm

In order to orient the liquid crystal molecules 10 as shown in FIG. 6,it is only necessary, as shown in FIG. 7, to regularly provide each ofthe orientation films 2 with fine grooves 11 of the pitch S. The grooves11 have depths ranging from 0.1 nm to several tens of nanometers and canbe made by photoresist exposure and etching as set forth, for example,in “Light control by grating structure smaller than wavelength”, byKikuta and Iwata, Optics, Vol. 27, No. 1, pp. 12-17, 1998. A model inwhich the grooves are formed by etching may be made and used to transferthe grooves to plastic.

Instead of a pattern shown In FIG. 7, a convexity or concavity 12 of agrating pattern such as that shown in FIG. 8 may be used if theorientation of the liquid crystal molecules 10 is uniform, looking at inthe x-y plane, that is, unless the refractive index of the liquidcrystal 1 varies with the orientation. This grating pattern may beformed not on the surfaces of the orientation films 2, but on thesurface of the transparent substrates 4 or 5. In this instance, theorientation films 2 can be dispensed with, as the case may be. The finegrooves 11 may be configured not as depressions but as projections.

As mentioned above, a liquid crystal lens in which the orientation ofthe liquid crystal molecules 10 is uniformed in the x-y plane to beindependent of polarization and to bring about a sharp focus can be usedas the variable optical-property element having the same structure as inFIG. 2, not only when the anisotropy of refractive index of the liquidcrystal is negative, but also when a positive nematic liquid crystal isused to satisfy the following condition:

ne>n₀  (5)

Substances having electrooptical effects and magnetrooptical effects ofmacromolecular dispersed liquid crystals, chiral smectic liquidcrystals, chiral cholesteric liquid crystals, ferroelectric liquidcrystals, antiferroelectric liquid crystals, and ferroelectrics are alsoapplicable to the present invention. Besides the above embodiment, theserespective substances are applicable to embodiments which will bedescribed later.

FIG. 9 illustrates a liquid crystal lens in which the electric field isapplied in the direction of the optical axis and a directionperpendicular thereto, and thereby the orientation of the molecules of aliquid crystal 14 is shifted with high speed. The liquid crystal 14 inthis figure, like that shown in FIG. 2, is constructed so that theanisotropy of refractive index is negative. This embodiment shows anvariable optical-property element (variable focal-length lens) providedwith members for applying one electric field, composed of the electrodes3, the AG power supply 8 connected thereto, the switch 9, and thevariable resistor 13, such as those shown in FIG. 2, and members forapplying another electric field, composed of electrodes 19 placedopposite to each other, sandwiching the optical axis 6 between them, anAC power supply 18 connected thereto, a switch 16, and a variableresistor 17. In this variable focal-length lens, that is, a liquidcrystal lens 15, FIG. 9 is in a state where the switch 9 is turned onand the switch 16 is off.

In order to change the focal length of the liquid crystal lens 15, asshown in FIG. 10, the switch 9 is turned off and at almost the sametime, the switch 16 is turned on. In this way, the electric field isapplied through the electrodes 19 to the liquid crystal 14, and themolecules of the liquid crystal 14 change their z direction to beparallel to the optical axis. Hence, the refractive Index of the liquidcrystal lens is increased and the function as a negative lens isimproved, thereby changing the focal length.

FIG. 11 shows the positions and shapes of the electrodes 19, looking atthe liquid crystal lens 15 from a+z direction.

FIGS. 12A and 12B show a modification example of the liquid crystal lensof FIG. 9, from which the electrodes 19 are different in position andshape. The electrodes 19, as shown in FIG. 12A, are provided in a stateof insulation from the transparent electrode 3 on the periphery of atleast one of the transparent substrates 4 and 5 shown in FIG. 12B, andbring about almost the same effect as those shown in FIG. 11.

The liquid crystal lens 15 depicted in FIG. 9 has the feature that wherethe z axis of each of the liquid crystal molecules 14 is made parallelto the optical axis 6, a response time is faster than in the liquidcrystal lens shown in FIG. 4. Whether the focal length of the liquidcrystal lens 15 is long or short, the electric field is applied to theliquid crystal molecules 14, and thus the liquid crystal lens 15 excelsin minimizing the variation of the orientation of the liquid crystalmolecules and the scattering of light.

In addition, the variable resistors 13 and 17 are properly adjusted, andthereby the focal length of the liquid crystal lens 15 can becontinuously changed. The orientation of the liquid crystal molecules 14lies in a state of a compromise between FIG. 9 in which the switch 9 ison and the switch 16 is off and FIG. 10 in which the switch 9 is off andthe switch 16 is on.

In the disclosure so far, reference has been made to a liquid crystalthat a dielectric anisotropy relative to the driving AC frequency of theliquid crystal molecules 10 or 14 is also negative as in the anisotropyof refractive index. As an example of such a liquid crystal, a discoticliquid crystal is cited.

In the embodiment shown in FIG. 13, a variable focal-length lens 21,instead of using the liquid crystal molecules 14 shown in FIG. 9, uses anematic liquid crystal 20, having a positive anisotropy of refractiveindex and dielectric anisotropy. Condition (5) is thus established.

In FIG. 13, an imaging device for digital cameras using the variablefocal-length lens 21 is shown. The molecules of the liquid crystal 20are helically oriented at the pitch P. The variable focal-length lens 21is such that the direction of one molecule of the liquid crystal 20 isnearly parallel to the x-y plane. If the value of the pitch P of theliquid crystal molecules is less than 20-60 times the wavelength λ oflight used in the variable focal-length lens 21, the liquid crystal 20can be practically thought of as an isotropic medium.

Now, it is assumed that the pitch P is smaller than the wavelength λ,that is, satisfies the following condition:

P<λ  (6)

In this case, the liquid crystal approaches the isotropic medium. Thisreason is as follows:

Now, it is assumed that the pitch P satisfies the following condition:

P<<λ  (5-1)

When the pitch P Is much smaller than the wavelength λ of light asmentioned above, the variable focal-length lens does not rely on thepolarization of incident light and functions as a medium with arefractive index n′:

n′=(ne+n ₀)/2  (5-2)

Subsequently, in accordance with the Jones' vector and matrix, adescription will be given of the reason why the nematic liquid crystal 1behaves effectively as an isotropic medium with the refractive index n′.

According to equations set forth in “Fundamentals of Liquid Crystals andDisplay Applications”, by K. Yoshino and M. Okazaki, Corona, pp. 85-92,a Jones' matrix W_(t) relative to the nematic liquid crystal with athickness d, shown in FIG. 13, including an absolute phase change exp(−iα), Is given by $\begin{matrix}{W_{t} = {^{- {i\alpha}}{{R\left( {- \Phi} \right)}\begin{bmatrix}{{\cos \quad X} - {i\frac{\Gamma}{2}\sin \quad \frac{X}{X}}} & {\Phi \sin \quad \frac{X}{X}} \\{{- \Phi}\sin \quad \frac{X}{X}} & {{\cos \quad X} + {i\frac{\Gamma}{2}\sin \quad \frac{X}{X}}}\end{bmatrix}}}} & \text{(5-3)}\end{matrix}$

where

Φ=2πd/P  (5-4)

Γ=2π(ne−n ₀)d/λ  (5-5)

α=2π{(ne+n ₀)/2}d/λ  (5-6)

X=(Φ²+Γ²/2)^(½)  (5-7)

$\begin{matrix}{{R\left( {- \Phi} \right)} = \begin{bmatrix}{\cos \quad \Phi} & {{- \sin}\quad \Phi} \\{\sin \quad \Phi} & {\cos \quad \Phi}\end{bmatrix}} & \text{(5-8)}\end{matrix}$

Here, when ordinary light is defined as polarized light in the directionof the minor axis of the liquid crystal molecule and extraordinary lightis defined as polarized light in the direction of the major axis of theliquid crystal molecule or in the direction in which the major axis isprojected on a plane parallel to the optical axis, Γ stands for a phasedifference between the ordinary light and the extraordinary light, dueto the nematic liquid crystal.

Also, Φ is the angle of twist of the liquid crystal molecules of thenematic liquid crystal 1 in radian. It is assumed that the coordinatesof Equations (5-3) and (5-8) are as x, y, and z axes shown in FIG. 13.Specifically, the x axis extends from the front side toward the backside of the plane of the figure and the y axis is the direction of themajor axis of the liquid crystal molecule at the entrance surface of thenematic liquid crystal.

Subsequently, consider how the Jones' matrix W_(t) of Equation (5-3)changes under Condition (5-1). Condition (5-1) can be rewritten as

0<P/λ<<1  (5-9)

Here, when P/λ approaches zero, find an ultimate value W_(t1) of theJones' matrix W_(t) of Equation (5-3).

Γ/Φ=(ne−n ₀)P/λ  (5-10)

and thus, when P/λ<<1,

|Γ/Φ|<<1  (5-11)

and when P/λ approaches zero, |Γ/Φ| also approaches zero.

Under Condition (5-11), the following approximations are accomplished:$\begin{matrix}{X = {{\Phi \sqrt{\left( {1 + \frac{\Gamma^{2}}{2\Phi^{2}}} \right)}} \approx {\Phi + \frac{\Gamma^{2}}{4\Phi}}}} & \text{(5-12)} \\{{\cos \quad X} \approx {\cos \left( {\Phi + \frac{\Gamma^{2}}{4\Phi}} \right)}} & \text{(5-13)} \\{{\frac{\Gamma}{2^{\prime}}\quad \frac{\sin \quad X}{X}} \approx {\frac{\Gamma}{2}\frac{\sin \left( {\Phi + \frac{\Gamma^{2}}{4\Phi}} \right)}{\Phi + \frac{\Gamma^{2}}{4}}}} & \text{(5-14)} \\{{\Phi \quad \frac{\sin \quad X}{X}} \approx \frac{\sin \left( {\Phi + \frac{\Gamma^{2}}{4\Phi}} \right)}{1 + \frac{\Gamma^{2}}{4\Phi^{2}}}} & \text{(5-15)}\end{matrix}$

When P/λ approaches zero, the following equations are obtained:

X →Φ  (5-16)

cos X →cos Φ  (5-17)

$\begin{matrix}\left. {\frac{\Gamma}{2}\quad \frac{\sin \quad X}{X}}\rightarrow 0 \right. & \text{(5-18)} \\\left. {\Phi \quad \frac{\sin \quad X}{X}}\rightarrow{\sin \quad \Phi} \right. & \text{(5-19)}\end{matrix}$

and thus, when P/λ approaches zero, the following equation is obtained:$\begin{matrix}{\left. W_{tL}\rightarrow{^{- {i\alpha}}{{R\left( {- \Phi} \right)}\begin{bmatrix}{\cos \quad \Phi} & {\sin \quad \Phi} \\{{- \sin}\quad \Phi} & {\cos \quad \Phi}\end{bmatrix}}} \right. = {^{- {i\alpha}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}}} & \text{(5-20)}\end{matrix}$

This is indeed the Jones' matrix of a medium which has the refractiveindex n′=(ne+n₀)/2 and the thickness d and is isotropic along theoptical axis. Thus, since P/λ<<1, the variable focal-length lens 21shown in FIG. 13 functions as the medium with the refractive index n′,and produces an image with no blurring.

Even where the liquid crystal has a compromise orientation of moleculesas shown in FIG. 15, the value of the refractive index ne is replaced bya refractive index ne′ of extraordinary light which is an intermediatevalue between the refractive indices ne and n₀, and thereby it ispossible to satisfy Conditions and Equations (5-3)-(5-20).

By constructing the liquid crystal lens as shown in FIG. 13, not only isthe voltage applied continuously and variably, but also the voltage tobe applied can be selected from among some discrete voltage values. Inthis case also, the variable focal-length lens is obtained.

Here, an actual example of the variable focal-length lens constructed asin FIG. 13 will be described in detail. Although the limit where P/λapproaches zero is given by Equation (5-20), the value of this limit maynot necessarily hold for an actual liquid crystal lens or a variablefocal-length lens. Thus, consider the approximation of Equation (5-3) tobe introduced. The following equations are established even in the casewhere P/λ≧1.

When Equation (5-3) is approximated, taking account of the first orderof P/λ, the following results are obtained. Specifically, when the firstorder of P/λ remains in Equations (5-12)-(5-14), that is, the firstorder of Γ/Φ remains in Equation (5-10) to neglect higher orders of P/λand Γ/Φ the following approximations are obtained: $\begin{matrix}{{{\cos \quad X} - {t\frac{\Gamma}{2}\quad \frac{\sin \quad X}{X}}} \approx {{\cos \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)} - {i\frac{\Gamma}{2\Phi}{\sin \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)}}}} & \text{(5-21)} \\{{\Phi \quad \frac{\sin \quad X}{X}} \approx {\sin \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)}} & \text{(5-22)}\end{matrix}$

From Equations (5-20), (5-21), and (5-22), the following equation isderived: $\begin{matrix}\begin{matrix}{W_{t} \approx \quad {^{{- i}\quad \alpha}{{R\left( {- \Phi} \right)}\begin{bmatrix}{{\cos \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)} - {i\frac{\Gamma}{2\Phi}{\sin \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)}}} & {\sin \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)} \\{- {\sin \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)}} & {{\cos \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)} + {i\frac{\Gamma}{2\Phi}{\sin \left( {\Phi + {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}}} \right)}}}\end{bmatrix}}}} \\{\equiv \quad W_{tN}}\end{matrix} & \text{(5-23)}\end{matrix}$

Hence, in order that the value of W_(tN) can be thought of as nearlyequal to the Jones' matrix of the isotropic medium, it is only necessaryto make the value of |iΓ/2 Φ| close to zero. In this case, W_(tN)approaches the following matrix: $\begin{matrix}{^{- {i\alpha}}\begin{bmatrix}{\cos \left( {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}} \right)} & {\sin \left( {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}} \right)} \\{- {\sin \left( {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}} \right)}} & {\cos \left( {\frac{\Gamma}{4}\frac{\Gamma}{\Phi}} \right)}\end{bmatrix}} & \text{(5-24)}\end{matrix}$

This equation means that the liquid crystal 1 rotates incident light byΓ/4·Γ/Φ for polarization, but can be thought of as the isotropic medium.Hence, a variable focal-length lens which does not cause the blurring ofan image will be obtained when satisfying the following equation:

|i(Γ/2Φ)|≈0  (5-25)

that is,

|Γ/2Φ|<0.11  (5-26)

From Equation (5-10), the following equation is derived: $\begin{matrix}{\frac{\Gamma}{2\Phi} = {\frac{1}{2}\left( {n_{e} - n_{0}} \right)\frac{P}{\lambda}}} & \text{(5-27)}\end{matrix}$

When the variable focal-length lens of the present invention is used foreach of lenses employed in relatively low-cost products of actualphotographing apparatuses with lenses, such as electronic cameras, VTRcameras, and electronic endoscopes, the number of pixels of thesolid-state image sensor is small and thus a high resolution may notnecessarily be required. Hence, Condition (5-26) can be moderated asfollows:

|Γ/2Φ|<1  (5-28)

Since the high resolution is required for lenses of an electronicphotographing apparatus with a large number of pixels and a product withhigh image quality, such as a film camera or a microscope, it isdesirable to satisfy the following condition:

|Γ/2Φ|<π/6  (5-29)

In the case of a lens which is not used for image formation as in anoptical disc, or an electronic photographing apparatus with a smallnumber of pixels, the condition is further moderated as follows:

|Γ/2Φ|<π  (5-30)

As is true of any embodiment, when the liquid crystal has a helicalarrangement or when the major axes of the liquid crystal molecules arenot perpendicular to the optical axis, namely oblique, it is onlynecessary to replace the refractive index ne corresponding to Equationsand Conditions (5-1) and (5-26)-(5-30) with the refractive index ne′.

Some design examples are cited below. If the thickness d of the nematicliquid crystal is too small, the power of the lens will be reduced andthe liquid crystal will be of no use as the lens. If it is too large,light will be scattered and flare will be caused. It is thus desirablethat the thickness d satisfies the following condition:

2μ<d<300μ  (5-31)

In view of visible light, the wavelength λ of light must be so chosen asto satisfy the following condition:

0.35μ<λ<0.7μ  (5-32)

Although the value of (ne−n₀) is governed by the physical properties ofthe liquid crystal, most substances satisfy the following condition:

0.01<|ne−n ₀|<0.4  (5-33)

First Design Example

d=15μ

λ=0.5μ

ne−n₀=0.2

P=0.06μ

then

Γ/2Φ=(½)·0.2×0.06/0.5=0.012

This satisfies Conditions (5-20) and (5-28)-(5-30).

Second Design Example

d=50μ

λ=0.6μ

ne−n₀=0.25

P=0.5μ

then

Γ/2Φ=(½)·0.5×0.25/0.6=0.1042

This satisfies Conditions (5-26) and (5-28)-(5-30).

Third Design Example

d=100μ

λ=0.55μ

ne−n₀=0.2

P=3μ

then

Γ/2Φ=(½)·0.2×3/0.55=0.5454

This satisfies Conditions (5-28) and (5-30).

Fourth Design Example

d=200μ

λ=0.95μ

ne−n₀=0.2

P=7μ

then

Γ/2Φ=(½)·0.2×7/0.95=0.737

This satisfies Conditions (5-28) and (5-30).

In each of the design examples mentioned above, the nematic liquidcrystal is used as an example. In order to make the pitch of twist ofthe nematic liquid crystal smaller than the wavelength of light used, itis good practice to mix a chiral dopant with the liquid crystal.

As the chiral dopants, cholesteric liquid crystals or optically active,synthetic compounds are used. The examples of the nematic liquidcrystals are shown In chemical formulas (a) and (b) described below andthe examples of the chiral dopants are shown in chemical formulas (c)and (d).

In Condition (5-30), when an example of a typical liquid crystal isconsidered as

ne−n ₀=0.1

it follows that

(½)×0.1 (P/λ)<π

From this result, the following condition is obtained:

P<20π·λ≈62.8μ  (5-61)

Similarly, substitution of ne−n₀=0.1 in Condition (28) gives

P<20μ  (5-62)

Hence, if a liquid crystal is constructed to satisfy Condition (5-61) or(5-62) in accordance with a product using the liquid crystal, thevariable optical-property element, such as the variable focal-lengthlens, with little blurring (flare) will be obtained. Conditions andEquations (5-1)-(5-30) hold for all the liquid crystals having thehelical structures with the pitch P as well as for the nematic liquidcrystals. As the examples of such liquid crystals, cholesteric liquidcrystals, smectic liquid crystals, ferro-electric liquid crystals, andantiferroelectric liquid crystals are cited.

FIG. 14 shows the variable focal-length lens 21 used in the imagingdevice shown in FIG. 14, looking at from the Z direction. Electrodes 22a, 22 b, 22 c, 23 a, 23 b, and 23 c divided into six pieces are placedclose to the periphery of the variable focal-length lens 21 and areinsulated from the transparent electrodes 3. These pairs of electrodes22 a and 23 a; 22 b and 23 b; and 22 c and 23 c are such that ACvoltages are applied in succession by a triple switch 24. In this way,the direction of the electric field is changed and thereby theorientation of the liquid crystal molecules becomes nearly isotropic. Ifthe electric field is applied in only one direction, the helicalstructure of the liquid crystal molecules may be disrupted.

Subsequently, a description is given of the operation of the imagingdevice shown in FIGS. 12 and 14. When the switch 9 is turned on, thetriple switch 24 is kept to an off state. Thus, the major axes of themolecules of the liquid crystal 20 become nearly parallel to the opticalaxis. In this case, a liquid crystal lens portion 25 becomes a negativelens with weak power.

Then, when the switch 9 is turned off and at the same time, the tripleswitch 24 is turned on, the electric field is applied in a lateraldirection to the liquid crystal 20, and thus the orientation of themolecules of the liquid crystal 20 is shifted with high speed as shownin FIG. 13.

For a period T for switching voltages applied to three electrodes of thetriple switch 24, there is the need to satisfy the followingrelationship. In the optical system shown in FIG. 13, when the tripleswitch 24 is in an off state and the switch 9 is in an on state andafter some time, is turned off, the molecules of the liquid crystal 20are naturally oriented as shown in FIG. 13 because of the orientationalregulating force of the orientation films 2, even though the tripleswitch 24 is not turned on. Thus, when a time required to naturallyorient the molecules as shown in FIG. 13 is represented by τ, it isnecessary to have the following relation:

T≦τ  (7)

If the period T is too large to satisfy Condition (7), there is the fearthat the helical structure of the molecules of the liquid crystal 20 maybe disrupted and the orientation of the molecules of the liquid crystal20 may be shifted to a homogeneous orientation parallel to theorientation films 2.

For Condition (7), it is only necessary to satisfy the followingcondition in practical use:

T≦1 0 τ  (7-1)

If this condition is not satisfied, much time may be required until themolecules of the liquid crystal 20 have a completely helical orientationwhen voltages applied to the electrodes 22 and 23 are low.

After the orientation of the molecules of the liquid crystal 20 has beenreturned to a state shown In FIG. 13, the triple switch 24 may be turnedoff discontinuously. In other words, the triple switch 24 may be kept toan on state only while the orientation of the molecules of the liquidcrystal 20 changes from a homeotropic orientation in a state parallelwith the optical axis 6 to the helical orientation shown in FIG. 13caused even when the switch 9 is turned off. Consequently, an electricpower can be saved, which is advantageous.

As shown in FIG. 15, the variable resistors 13 and 17 are properlyadjusted so that the molecules of the liquid crystal 20 are oriented tobe oblique with respect to the optical axis, and thereby the focallength of the variable focal-length lens 21 can be continuously changed.That is, this lens is convenient for use in a zoom lens system.

FIG. 16 shows an embodiment in which the variable focal-length lensshown in FIG. 13 or 15 is used in a zoom lens system. In this figure,each of reference numerals 21A and 21B corresponds to the variablefocal-length lens 21 shown in FIG. 13. The variable focal-length lenses21A and 21B are front and rear lens units respectively arranged beforeand behind a stop 26. That is, this zoom lens system includes the frontlens unit with negative refracting power, composed of the variablefocal-length lens 21A having a negative function and the rear lens unitwith positive refracting power, as a whole, composed of the stop 26, thevariable focal-length lens 21B having a positive function, and apositive lens 29. By changing the focal lengths of the variablefocal-length lenses 21A and 21B without mechanically moving individuallenses, the focal length of the entire lens system and the movement ofan image plane can be corrected. Likewise, the focusing operation can beperformed. In this embodiment, when the variable focal-length lens 21AIs energized to change the focal length, the strength of the electricfield applied to a liquid crystal 25 b is not changed, but the frequencyof the electric field is changed to four stages of f₁, f₂, f₃, and f₄.In this way, a liquid crystal in which the sign of the dielectricanisotropy changes with the frequency is used. When the frequencies f₁,f₂, f₃, and f₄ are determined as f₁<f₂<f₃<f₄, the dielectricanisotropies of the liquid crystal 25 b are so chosen as to have signsopposite to each other at the frequencies f₁ and f₄.

In this zoom lens system, the frequency is changed by turning the switch24. In this case, electrodes 22F may be eliminated. The frequencies f₁,f₂, f₃, and f₄, instead of being changed gradually, may be changedcontinuously. Moreover, when the frequency is changed, the strength ofthe electric field may also be changed at the same time.

Each of the liquid crystal lenses 21A and 21B may use not only thehelical liquid crystal, but also the macromolecular dispersed liquidcrystal in which a liquid crystal that the dielectric anisotropy varieswith the frequency is dispersed among macromolecules. The variablefocal-length lens 21B is an example of the variable optical-propertyelement using the macromolecular dispersed liquid crystal.

An AC power supply 9 e capable of continuously changing the frequency isconnected to the two electrodes 3. The frequency of the AC power supplyis varied and thereby the focal length of the optical element can bechanged.

By associating the liquid crystal lens 21A with the liquid crystal lens21B, the zooming operation can be performed. In addition, if only theliquid crystal lens 21B is energized, the focusing operation can beperformed.

Electrodes 22G need not necessarily be used, or voltages applied to theelectrodes 22G may be changed in association with a change of afrequency f of the AC power supply 9 e.

In the imaging device shown in FIG. 13, the liquid crystal lens, insteadof using the liquid crystal 20, may use the chiral cholesteric liquidcrystal, chiral smectic liquid crystal, ferro-electric liquid crystal,antiferroelectric liquid crystal, liquid crystal with the negativeanisotropy of refractive index, ferro-electric macromolecular dispersedliquid crystal, etc. Conditions (5-26), (5-28)-(5-30), (5-61), (5-62),(6), (7), and (7-1) also hold for the case where each of these liquidcrystals is used.

An optical system shown in FIG. 17 is such that, instead of the liquidcrystal 20 of FIG. 13, cells with the average diameter D includingnematic liquid crystal molecules 34 are arranged granularly in apolymer. In this embodiment, the divided electrodes 22 and 23 areactuated as in FIG. 13, but are arranged on the peripheries of lenses 32and 33 so that they are insulated from the transparent electrodes 3. Theoperation of the triple switch 24 is the same as in the optical systemof FIG. 13.

In the optical system shown in FIG. 17, when the switch 9 is in an onstate, the liquid crystal molecules 34 hold an homeotropic orientation,while when the switch 9 is turned off and the triple switch 24 is on,the electric field is applied to the liquid crystal molecules 34 in alateral direction, and the liquid crystal molecules 34, althoughsomewhat random, are oriented parallel to the x-y plane with high speedas shown in FIG. 18. Conditions (7) and (7-1)) also hold for the opticalsystem shown in FIGS. 17 and 18.

As mentioned above, the liquid crystal molecules 34, as in FIG. 18, areoriented nearly perpendicular to the optical axis 6, and thus' thisliquid crystal lens excels in bringing about a greater change of therefractive index of a liquid crystal 35.

Here, if the average diameter D of the liquid crystal molecules 34satisfies the following condition, the scattering of light can beprevented, which is favorable:

D<λ/5  (8)

Where the thickness of the liquid crystal 35 is relatively small, thereis no problem in practical use if the diameter D satisfies the followingcondition, instead of Condition (8):

 D<2λ  (8-1)

Now, the volume ratio between the liquid crystal 35 and the liquidcrystal molecules 34 is represented by ff. In order to bring about asufficient effect as the variable focal-length lens, it, is desirable tosatisfy the following condition:

0.5<ff<0.999  (9)

If the value of the ratio ff exceeds the upper limit of Condition (9),the amount of polymer will be so reduced that the fine cells of theliquid crystal molecules 34 cease to be formable. Below the lower limit,the effect of the variable focal-length, namely the amount of change ofthe focal length is reduced.

In an attempt to increase the amount of polymer so that the liquidcrystal 35 approaches a solid phase, it is desirable to satisfy thefollowing condition, instead of Condition (9):

0.1<ff<0.5  (9-1)

FIG. 19 shows the embodiment of an optical system in which therefractive index of a liquid crystal is changed by temperature in thepresent invention. At a transition temperature Tc or less, a nematicliquid crystal 36 having a positive anisotropy of refractive index, asillustrated in FIG. 19, shows the homeotropic orientation in which themajor axes of molecules point in the z direction and lies in a state ofthe refractive index n₀ which is relatively low. In this case, theswitch 9 is in an on state.

When a switch 43 of a heater 41 is turned on and the liquid crystal 36is heated by the heater 41 so that the temperature of the molecules ofthe liquid crystal 36 becomes higher than the transition temperature Tc,as shown in FIG. 20, the liquid crystal 36 changes to a transparentliquid in which the molecules of the liquid crystal 36 move randomly. Inthis case, the switch 9 is kept in an off state. In a state of FIG. 20,the refractive index n of the liquid crystal 36 is given by

n=(2n ₀ +ne)/3  (10)

In other words, the refractive index n of the liquid crystal becomeshigher and consequently, the refracting power of a positive lens 32 b isstrengthened.

In a state of FIG. 19, if the orientational regulating force by theorientation films 2 is sufficient, the switch 9 way be turned off.However, when the switch 9 is turned on, the molecules of the liquidcrystal 36 are regularly arranged, and thus the scattering of lightcaused by the molecules of the liquid crystal 36 can be prevented, whichis favorable.

In order to cause a liquid phase transition to the liquid crystal, theoptical system uses the heater 41 for heating, but the frequency of theAC power supply may be increased to thereby heighten vibrations of themolecules of the liquid crystal 36 so that the temperature is raised andthe phase transition is made.

The variable optical-property element of the present invention statedabove is constructed so that the strength and direction of the electricfield are mainly varied to thereby change the orientation of themolecules of the liquid crystal constituting the optical element.However, the orientation of the liquid crystal can be shifted not onlyby varying the strength of the electric field, but also by changing thefrequency of the electric field. Moreover, the orientation of themolecules of the liquid crystal can also be shifted by changing thestrength of the magnetic field.

Techniques of shifting the orientation of the molecules of the liquidcrystal by changing the frequency of the electric field applied to theliquid crystal and of changing the strength of the magnetic fieldapplied to the liquid crystal as mentioned above are applicable to theoptical systems cited as examples in FIGS. 2, 4, 9, 10, 13, 16, 17, and20, and FIG. 21 described below.

In the technique of shifting the orientation of the molecules of theliquid crystal by changing the frequency of the electric field, the useof a liquid crystal in which the positive sign of the anisotropy ofrefractive index is replaced with the negative sign is particularlyadvantageous because the orientation of the molecules of the liquidcrystal can be shifted with high speed in accordance with the change ofthe frequency of the electric field.

FIG. 21 shows a lens in which the refractive index is changed by themagnetic field H. In this figure, reference numeral 45 denotes a lens;46, a substance possessing a magnetrooptical effect; 47, substrates; 48,orientation films; 49A, a switch; 49B, an AC power supply; 49C, avariable resistor; 49D, a coil; and 49E, an iron core.

As an example of the substance 46, lead glass, quartz, or a liquidcrystal is cited. In the case of the liquid crystal, it is favorable touse the orientation films 48.

In order to shift the orientation of the molecules of the liquid crystalwith high speed, It is desirable to previously applying some degree ofvoltage instead of removing the voltage. In this way, where theorientation is changed, the voltage is made higher and thereby theorientation can be shifted with high speed.

The embodiment shown in FIG. 13, which is the imaging device for digitalcameras of the present Invention using the variable optical-propertyelement, will be described in more detail below.

In FIG. 13, an optical system 31 is placed which is constructed with thevariable focal-length liquid crystal 21 including the liquid crystallens portion 25 and a negative lens 28 and a positive lens 29 behind thestop 26. The positive lens 29 is provided for the purpose of rendering achief ray incident perpendicular or nearly perpendicular to asolid-state image sensor 30, for example, at an angle of 90±20° with thelight-receiving surface of the image sensor. The negative lens 28 isprovided the purpose of improving the Petzval sum to correct curvatureof field. A positive lens 27 situated on the side of the stop 26 (theentrance side) is such that its object-side surface is convex andthereby spherical aberration is favorably corrected. The liquid crystallens portion 25 assumes the shape of a negative lens to correctchromatic aberration. One of the surfaces of the lenses 27, 28, and 29is configured to be aspherical and thereby aberrations can be morefavorably corrected. It is desirable that the liquid crystal lensportion 25 is located close to the stop 26 because the effectivediameter of the liquid crystal lens portion 25 can be diminished and thethickness can be reduced.

When the orientation of the molecules of the liquid crystal 20 in theliquid crystal lens portion 25 is shifted, the aberration of the opticalsystem 31 including the positive lens 27, the liquid crystal lensportion 25, the negative lens 28, and the positive lens 29 fluctuates,and the scattering of light caused by the liquid crystal lens portion 25varies, thereby changing the MTF (modulation transfer function) of theoptical system 31.

The imaging device shown in FIG. 13 is designed so that the change ofthe MTF caused by the fluctuation of the aberration and the variation ofthe scattering of light is compensated by an electronic circuit. Thatis, the compensation for the change of the MTF caused when the focallength of the liquid crystal lens 21 is change to perform the focusingoperation due to a shift of the position of an object is made by varyingan enhance circuit or an image processing circuit in a circuit system44. Specifically, it is only necessary to use a means of changing thecharacteristics of a digital filter like a Wiener filter or changing theamount of edge enhance of the enhance circuit. Here, the change of theNTF may be derived from the design data of the optical system 31 or theamount of compensation of the MTF may be changed by actually measuringeach camera.

FIG. 22 shows a diagram in which a range measurement on an infraredprojecting, active range finding technique is made with respect to thecompensation by the electronic circuit. On distance information derivedhere, the amount of enhance is selected to compensate the change of theMTF of the liquid crystal lens. Subsequently, the digital filter is usedand the final image is obtained.

FIG. 23 shows a digital camera 50 using an extended surface prism 51 (aprism having extended surfaces) in the present invention. Referencenumeral 52 represents a variable focal-length mirror; 53, a thin filmcoated with aluminum; 54, an electrode; 55, a solid-state image sensor;56, a substrate; 57, a power supply; 58, a switch; and 59, a variableresistor.

As an example of the variable focal-length mirror 52, a membrane mirroris cited which is set forth in “Quick focusing of imaging optics usingmicromachined adaptive mirrors”, by Gleb Vdovin, Optics Communications,Vol. 140, pp. 187-190, 1997. When a voltage is applied across theelectrode 54, the thin film 53 is deformed by an electrostatic force andthe focal length of a reflecting mirror is changed. In this way, afocusing adjustment can be made. Light 60 from an object is refracted bysurfaces R₁ and R₂, and after being reflected by the reflecting mirror(thin film) 53 and a surface R₃ of the extended surface prism 51, isrefracted by a surface R₄ and falls on the solid-state image sensor 55.

Thus, this device constructs an imaging optical system with the extendedsurfaces R₁, R₂, R₃, and R₄ and the reflecting mirror 53. In particular,by optimizing the shapes of the extended surfaces R₁, R₂, R₃, and R₄,aberration of an object image is reduced to a minimum.

In the imaging device of FIG. 23, in order to correct astigmatism, it isdesirable that the aperture of the reflecting mirror is shaped into anelliptic form which has its major axis along the direction of the yaxis, that is, of a line that a plane including incident light on thereflecting mirror 52 and emergent light therefrom crosses the reflectingmirror 52. In this figure, the reflecting mirror 52, the thin film 53,and the solid-state image sensor 55 are constructed to be independent ofone another and placed on the substrate 56. Since, however, thereflecting mirror 52 and the thin film 53 can also be fabricated througha silicon lithography process, the substrate 56 may be constructed ofsilicon so that at least one part of the reflecting mirror 52 isfabricated, together with the solid-state image sensor 55, on thesubstrate 56 by the lithography process.

In this way, the reflecting mirror 52 is integrated with the imagesensor 55, and this is advantageous for compactness and a reduction incost. Moreover, the reflecting mirror 52 may be constructed with afixed-focus mirror. In this case also, the reflecting mirror 52 can bemade through the lithography process.

A reflection type liquid crystal display or a transmission type liquidcrystal display, although not shown in the figure, may be constructedintegrally with the substrate 56 through the lithography process. Thesubstrate 56 may be made of glass, and it is only necessary to constructthe solid-state image sensor and the liquid crystal display on thisglass substrate through the technique, for example, of a thin filmtransistor. The extended surface prism 51 is configured with plastic orglass molding and thereby curved surfaces of any desired shape can beeasily configured and fabrication is simplified.

FIG. 24 shows another digital camera using the extended surface prism51. This digital camera, instead of using the reflecting mirror 52 ofthe digital camera in FIG. 23, uses a variable focal-length mirror 61.The variable focal-length mirror 61 is provided integrally with theextended surface prism 51 on the surface R₂ of the prism 51. Thevariable focal-length mirror 61 is comprised of a reflecting mirror 62,transparent electrodes 63, one of which is provided on the surface R₂ ofthe prism 51, and orientation films 64 and 65 and has a liquid crystal66 between the orientation films 64 and 65. Here, the variablefocal-length mirror 61 may be constructed to be independent of theextended surface prism 51 so that both are cemented or the electrode 63and the orientation film 64 may be provided on the surface R₂ of theprism 51.

The light 60 incident on the digital camera from the object, as in FIG.23, is refracted by the surfaces R₁ and R₂ and after being reflected bythe reflecting mirror 62, passes through the orientation film 65, theliquid crystal 66, the orientation film 64, and the transparentelectrode 63 to enter the extended surface prism 51. After reflection bythe surface R₃ and emergence from the surface R₄, the light falls on thelight-receiving surface of the solid-state image sensor 55. Here, whenthe voltage applied to the variable focal-length mirror 61 is varied,the focal length of the mirror 61 is changed and thus the focusingadjustment can be made.

The macromolecular dispersed liquid crystal is used for the liquidcrystal 66 of the variable focal-length mirror 61. As described inconnection with FIGS. 16-18, the electric field applied to the liquidcrystal 104 is changed and thereby the situation is changed, forexample, from FIG. 17 to FIG. 18. Consequently, the refractive index ofthe liquid crystal is changed and the focal length of the variablefocal-length mirror is varied.

The digital camera shown in FIG. 24 has the same function as a digitalcamera using the liquid crystal lens of FIG. 17 even though theelectrodes 22 and 23 of FIG. 17 are not used. Specifically, in FIG. 24,when the switch 58 is turned off, the molecules of the liquid crystalare oriented randomly in a state of high refractive index. Hence, thevariable focal-length mirror 61 has a strong function of converging thelight. Here, when the switch 58 Is turned on, the molecules are orientedin one direction, and thus the refractive index becomes lower, reducingthe function of converging the light. In this way, the focusingadjustment of the variable focal-length mirror 61 is performed. If atleast two variable focal-length mirrors 61 are used in the extendedsurface prism 51, this device can be used as a zoom lens system.

The variable focal-length mirror 52 shown in FIG. 23 may be replacedwith the variable focal-length mirror 61 of FIG. 24. In this case, theorientation films 64 and 65 need not necessarily be used. In addition,the transparent electrode 63 may be substituted by the reflecting mirror62 also used as an electrode which is constructed as the liquid crystaloptical element of the variable focal-length mirror 61. Instead of themacromolecular dispersed liquid crystal 66, the nematic liquid crystalof a helical orientation, as well as the cholesteric liquid crystal andthe smectic liquid crystal, may be used.

FIG. 25 shows an example in which a diffraction optical element 70 isused instead of the reflecting mirror 52 or the variable focal-lengthmirror 61 shown in FIG. 23 or 24. The diffraction optical element 70 isconstructed with a diffraction surface 71 configured on a reflectingmirror 72, a transparent electrode 73, an orientation film 74, and aliquid crystal 75.

In a digital camera 76 shown In FIG. 25, the light 60 from the object,as in the above embodiment, is incident on the extended surface prism51, and after being transmitted through the prism 51, enters thediffraction optical element 70. The light, after being diffracted by thediffraction surface 71, leaves the diffraction optical element 70 and isagain incident on the extended surface prism 51. By being reflected asshown in the figure, the light emerges from the prism 51 and falls onthe solid-state image sensor 55.

Here, when a switch 77 is turned on, the orientation of the molecules ofthe liquid crystal 20 is shifted so that the molecules are oriented in avertical direction, and the order of diffraction of the diffractionoptical element 70 is changed. In this way, the focal length is variedand the focusing operation can be performed. In this case, the pitch ofthe molecules of the liquid crystal 20., as in FIG. 13, satisfiesCondition (6). In this embodiment, the diffraction surface 71 isconfigured as a reflecting surface, and a reflection type diffractionoptical element is presented.

FIG. 26 illustrates variable focal-length spectacles, each having thevariable focal-length lens. The variable focal-length lens is used as aneyeglass lens. The variable focal-length lens including lenses 30H and31H, the orientation films (not shown), and the electrodes (whose partis not shown) is attached to a frame 79 of the spectacles.

In this variable focal-length lens, the electrodes 22 and 23, as in FIG.16, are provided on the peripheries of the lenses 30H and 31H. When theelectrodes 22 and 23 are configured as transparent electrodes, theperiphery of the visual field of the spectacles becomes bright, which isfavorable.

In the embodiments mentioned above, the variable focal-length lens ischiefly used as the variable optical-property element, but a diffractionoptical element, Fresnel lens, prism, or lenticular lens may be used asthe variable optical-property element. It is merely necessary that aportion subjected to the diffraction or reflection of light,constituting each element, is replaced by a variable refractive-indexsubstance, that is, a liquid crystal, ferro-electric, or substancepossessing an electrooptic effect. In order to shift the orientation ofthe molecules of the liquid crystal, the frequency of an electric ormagnetic field may be changed.

The optical system using the variable optical-property element of thepresent invention stated above can be employed in a photographing devicein which an object image is formed and received by an image sensor, suchas a CCD or a silver halide film, for photography, notably a camera oran endoscope. Furthermore, the optical system can also be used as anobservation device for observing an object image through an eyepiece,and in particular, as an objective optical system which is a part of thefinder of a camera. The embodiments of such optical systems aredescribed below.

In FIGS. 27, 28, and 29, an electronic camera 80 includes aphotographing optical system 81 having a photographing optical path 82,a finder optical system 83 having a finder optical path 84, a release85, a flash lamp 86, and a liquid crystal display monitor 87. When therelease 85 provided on the upper side of the camera 80 is pushed,photography is performed through a photographing objective opticalsystem 88 in association with the operation of the release 85. Thephotographing objective optical system 88 is provided with a pluralityof transmission type variable optical-property elements (using liquidcrystals here, indicated by hatching portions in the figure) to performthe zooming and focusing operations. An object image formed by theobjective optical system 88 falls on an imaging surface 90 of a CCD 89through a filter 91 such as a low-pass filter or an infrared cutofffilter. The object image received by the CCD 89 is displayed as anelectronic image, through a processing means 92, on the liquid crystaldisplay monitor 87 provided on the back side of the camera 80. Theprocessing means 92 has a memory and is also capable of recording theelectronic image photographed. Also, this memory may be provided to beindependent of the processing means 92 or may be designed toelectronically execute record/write with a floppy disk. The camera maybe constructed as a silver halide film camera provided with a silverhalide film instead of the CCD 89.

Moreover, on the finder optical path 84, an imaging optical systemprovided with reflection type variable optical-property elements 66H isplaced as a finder objective optical system 93. A cover lens 94 withpositive power is provided as a cover member to enlarge an angle ofview. The cover lens 94 and a prism VP1 situated on the object side of astop S of the imaging optical system constitute a front lens unit GF ofthe finder objective optical system 93, while a prism VP situated on theimage side of the stop S constitutes a rear lens unit GR thereof. Thevariable optical-property elements 66H are arranged respectively in thefront and rear lens units GF and GR sandwiching the stop S therebetween,and thereby the zooming and focusing operations are performed. Thisoptical system uses the reflection type variable optical-propertyelements, each of which is constructed integrally with a reflectingprism. The liquid crystals 66H are used in these elements, and thezooming and focusing operations are performed by changing the opticalproperty as mentioned above. The control of the properties of eachliquid crystal is made by the processing means 92 in association withthe zooming and focusing operations of the photographing objectiveoptical system. An object image formed by the finder objective opticalsystem 93 is placed on a field frame 97 of a Porro prism 95 which is animage erecting member. The field frame 97 separates a first reflectingsurface 96 of the Porro prism 95 from a second reflecting surface 98,and is interposed between them. An eyepiece optical system 99 whichintroduces an erect image into an observer's eye E is placed behind thePorro prism 95.

In the camera 80 designed as mentioned above, the finder objectiveoptical system 93 can be constructed with a small number of opticalmembers, and high performance and compactness are achieved. Furthermore,since the optical path of the objective optical system 93 can be bent,the number of degrees of freedom of layout in the camera is increased,and this is advantageous for design.

FIG. 30 shows a case where the imaging optical system of the presentinvention is Incorporated in the objective optical system 88 of thephotographing section of the electronic camera 80. In this case, thephotographing objective optical system 88 situated on the photographingoptical path 82 is an imaging optical system using the reflection typevariable optical-property elements. An object image formed by thephotographing objective optical system 88 falls on the imaging surface90 of the CCD 89 through the filters 91 such as a low-pass filer and aninfrared cutoff filter. The object image received by the CCD 89 isdisplayed as an electronic image, through the processing means 92, on aliquid crystal display (LCD) 100. The processing means 92 also controlsa recording means 101 which records the object image obtained by the CCD89 as electronic information. The object image displayed on the LCD 100is introduced through the eyepiece optical system 99 into the observer'seye E. The eyepiece optical system 99 includes a decentered prism VP3provided with the variable optical-property element 66H which has thesame aspect as that used in the imaging optical system of the presentinvention. By controlling the properties of the element 66H, the depthof a virtual image in the LCD 100 can be adjusted in accordance with thediopter of the observer. The prism VP3 includes an entrance surface 102,a reflecting surface 103, and a surface 104 used for both reflection andrefraction. At least one of the surfaces 103 and 104 having tworeflecting functions, preferably both, are constructed with symmetricalextended surfaces, each of which provides a light beam with power andhas only one symmetrical surface for correcting decentered aberration.Such symmetrical surfaces are situated on nearly the same plane as thoseof the symmetrical extended surfaces of the decentered prisms VP1 andVP2 which are arranged in the front and rear lens unit GF and GR of thephotographing objective optical system 88.

FIG. 31 shows another case where the imaging optical system of thepresent invention, as in FIG. 30, is incorporated in the objectiveoptical system 88 of the photographing section of the electronic camera80. In this case, an eyepiece optical system 99B is different from theeyepiece optical system 99 of FIG. 30. Specifically, the electroniccamera 80 shown in FIG. 31 is provided with the variable focal-lengthlens 21, such as that shown in FIG. 13, in the proximity of the exitsurface 104 of the decentered prism VP3 in the eyepiece optical system99 of FIG. 30. In this way, the decentered prism VP3 is combined withthe variable focal-length lens 21, and thereby both the conversion ofdiopter by the decentered prism and the change of magnification by thevariable focal-length lens can be carried out.

In the camera 80 designed as mentioned above, the photographingobjective optical system 88 can be constructed with a small number ofoptical members, and high performance and compactness are achieved. Inaddition, since the entire optical system is placed in the same plane,the thickness of the camera in a direction perpendicular to this planecan be reduced.

FIGS. 32A and 32B show an electronic endoscope in which the variableoptical-property element of the present invention is incorporated in anoptical system 120. In this case, an objective optical system 125 forobservation uses an imaging optical system provided with reflection typevariable optical-property elements 128 for performing the zooming andfocusing operations. An electronic endoscope system, as shown in FIG.32A, includes an electronic endoscope 111; a light source device 112 forsupplying illumination light; a video processor 113 for processing asignal with respect to the electronic endoscope 111; a monitor 114 fordisplaying an image signal output from the video processor 113; a VTRdeck 115 and a video disk 116 for recording the image signal, eachconnected to the video processor 113; and a video printer 117 forprinting out the video signal as an image. A distal end 119 of aninserting section 118 of the electronic endoscope 111 is constructed asshown in FIG. 32B. An illumination light beam from the light sourcedevice 112 passes through a light guide fiber bundle 126 and illuminatesa part to be observed, through an objective optical system 127 forillumination. Light from the part to be observed is such that an objectimage is formed through a cover member 124 by the objective opticalsystem 125 for observation. The object image falls on an imaging surface123 of a CCD 122 through filters 121 such as a low-pass filter and aninfrared cutoff filter. Subsequently, the object image is converted intoan image signal by the CCD 122. This image signal is displayed directlyon the monitor 114 by the video processor 113 shown in FIG. 32A, and isrecorded in the VTR deck 115 and the video disk 116 and printed out asan image by the video printer 117. The endoscope designed in this waycan be constructed with a small number of optical members, irrespectiveof the fact that zooming and focusing functions are retained, and iscapable of achieving high performance and compactness.

Each of the decentered prisms provided in the front and rear lens unitsof the imaging optical system is of a two-internal-reflection type,including, three optical surfaces, one of which has the functions oftotal reflection and of refraction. However, the decentered prism usedIn the present invention is not limited to such a structure.

In the imaging device of the present invention described above, theimaging device shown in FIG. 23, for example, is provided with theoptical system including the extended surfaces and the variablefocal-length mirror. However, these extended surfaces can also be usedin the optical systems of other imaging devices using the variableoptical-property elements. It is possible to use such extended surfaces,for example, in the optical system of the imaging device using thevariable focal-length lens depicted in FIG. 13. In other words, theextended surfaces are applicable to optical systems, imaging opticalsystems, optical devices, and observation devices which use variableoptical-property elements in addition to variable optical-propertyreflecting mirrors.

The optical system of the present invention is used as an eyepieceoptical system, a finder optical system, the lens system of anelectronic imaging device (in FIG. 16, for example), and the lens systemof a digital camera imaging device.

A few examples of the variable focal-length prisms which can be used inthe present invention are shown in FIGS. 33-35. Although in any case theprism VP forming an image on an image plane 136 is depicted in thefigure, the prism VP can also be used in such a way that the directionof the optical path is reversed, that is, rays of light from an objectare rendered incident from the side of the image plane 236 to form theimage on the side of a pupil 131. The prism VP may be designed toconstruct an imaging optical system or an observation optical system byitself. Which of the surfaces of the prism should be used for thevariable optical-property element may be determined in accordance withthe application of the prism.

In FIG. 33, the prism VP includes a first surface 132, a second surface133, a third surface 134, and a fourth surface 135. Light passingthrough the entrance pupil 131, after being refracted by the firstsurface 132 to enter the prism VP, is internally reflected by the secondsurface 133 and enters the third surface 134 for internal reflection.The light is then incident on the fourth surface 135 and is refractedthere to form an image on the image plane 136. The variableoptical-property elements are provided on the second and third surfaces133 and 134, and thereby zooming and focusing become possible.

In FIG. 34, the prism VP includes the first surface 132, the secondsurface 133, the third surface 134, and the fourth surface 135. Lightpassing through the entrance pupil 131, after being refracted by thefirst surface 132 to enter the prism VP, is internally reflected by thesecond surface 133 and enters the third surface 134 for totalreflection. The light is then incident on the fourth surface 135 and isinternally reflected there. Finally, the light is incident again on thethird surface 134 and is refracted there to form an image on the imageplane 136. In this case, the variable optical-property elements are usedfor the second and fourth surfaces 133 and 135.

In FIG. 35, the prism VP includes the first surface 132, the secondsurface 133, the third surface 134, and the fourth surface 135. Lightpassing through the entrance pupil 131, after being refracted by thefirst surface 132 to enter the prism VP, Is Internally reflected by thesecond surface 133 and enters the third surface 134 for internalreflection. The light is then incident again on the second surface 133and is internally reflected there. Finally, the light is Incident on thefourth surface 135 and is refracted there to form an image on the imageplane 136. In this case, the variable optical-property elements are usedfor the second and third surfaces 133 and 134.

The variable optical-property element of the present invention can beutilized for an image display. In FIGS. 36 and 37, a decentered prismoptical system in which the reflection type variable optical-propertyelement of the present invention is used for diopter adjustment, asshown in FIG. 37, is used as an eyepiece optical system 140. A pair ofcombinations, each including the eyepiece optical system 140 and animage display element 141, is provided so that the combinations areseparated by an interpupillary distance and supported, therebyconstructing a portable image display 142 such as a stationary or headmounted image display which is observable with the eyes.

Specifically, the display body 142 is provided with a pair of eyepieceoptical systems 140 for the eyes and, opposite thereto, has the imagedisplay elements 141, such as liquid crystal display elements, at theposition of the image plane. Moreover, the display body 142, as shown inFIG. 36, has a temple frame 143 which extends continuously on both sidesso that the display body 142 can be retained before an observer's eyes.

A speaker 144 is attached to the temple frame 143 so that an observercan enjoy not only an image observation, but also a stereoscopic sound.In this way, since the display body 142 having the speaker 144 isconnected through an image sound transmitting cord 145 to a videoreproducing device 136 such as a portable video cassette, the observer,as shown in the figure, is capable of holding the reproducing device 146at any position of his belt to enjoy an image sound. In FIG. 36,reference numeral 147 represents a control section for the switch andvolume of the reproducing device 146. Also, electronic parts such asimage and sound processing circuits are housed in the display body 142.

The cord 145 may be designed so that its tip as a jack can be attachedto the existing video deck. Moreover, it may be connected to a tuner forTV electric wave reception to watch TV, or may also be connected to acomputer so as to receive the image of computer graphics or a messageimage from the computer. To remove a cord which is obstructive to theoperation, an antenna may be provided to receive a signal from theoutside through the electric wave.

As is true of the whole of the present invention, each of the eyepieceoptical system, the finder optical system, the lens system of theelectronic imaging device (in FIG. 16, for example), and the lens systemof the digital camera imaging device is cited as an example of theimaging optical system. Also, the optical apparatus refers to anapparatus having an optical system.

The optical apparatus of the present invention shown in FIG. 38 isconstructed as an electronic imaging unit 180 using lenses 181, 182, and183, a prism 184, and a mirror 185.

The reflecting mirror 52 is constructed so that, like the membranemirror set forth, for example, in Optics Communications mentioned above,when a voltage is applied across the thin film 53 and the electrode 54,the thin film 53 is deformed by an electrostatic force to change thefocal length of a reflecting mirror, and thereby the focusing adjustmentcan be made. In the optical apparatus of this embodiment, the light 60from the object is refracted by the entrance and exit surfaces of thelenses 181 and 182 and the prism 184 for optical elements, and isreflected by the reflecting mirror 52. The light is then reflected bythe reflecting surface of the mirror 185, and after being refracted bythe lens 183, enters the solid-state image sensor 55.

In this way, the optical apparatus of this embodiment is designed sothat the imaging optical system is constructed with the optical elements181, 182, 183, 184, and 185 and the reflecting mirror 52. In particular,the surfaces of thicknesses of individual optical elements areoptimized, and thereby aberration of an object image can be reduced to aminimum.

In the optical apparatus shown in FIG. 38, in order to correctastigmatism, it is desirable that the aperture of the reflecting mirror52 is shaped into an elliptic form which has its major axis along thedirection of the y axis, that is, of a line that a plane includingincident light on the reflecting mirror 52 and emergent light therefromcrosses the reflecting mirror 52. The reflecting mirror 52 and thesolid-state image sensor 55 are constructed to be independent of eachother and placed on the substrate 56. Since, however, the reflectingmirror 52 can also be fabricated through a silicon lithography process,the substrate 56 may be constructed of silicon so that at least one partof the reflecting mirror 52 is fabricated, together with the solid-stateimage sensor 55, on the substrate 56 by the lithography process.

In this way, the reflecting mirror 52 which is one of the opticalelements is integrated with the image sensor 55, and this isadvantageous for compactness and a reduction in cost. Moreover, thereflecting mirror 52 may be constructed with a fixed-focus mirror. Inthis case also, the reflecting mirror 52 can be made through thelithography process. Here, a combination of the reflecting mirror 52,the solid-state image sensor 55, and the substrate 56 is referred to asa platelike unit 186. The platelike unit is an example of the opticalapparatus.

A display element, such as a reflection type liquid crystal display or atransmission type liquid crystal display, although not shown in thefigure, may be constructed integrally with the substrate 56 through thelithography process. The substrate 56 may be made of a transparentmaterial such as glass or quartz. In this case, it is only necessary tofabricate the solid-state image sensor and the liquid crystal display onthis glass substrate through the technique, for example, of a thin filmtransistor. Alternatively, this display element may be madeindependently and placed on the substrate 56.

The optical elements 181, 182, 183, 184, and 185 are configured withplastic or glass molding and thereby curved surfaces of any desiredshape can be easily configured and fabrication is simplified. In theimaging device of this embodiment, only the lens 181 is separated fromthe prism 184. but if the optical elements 182, 183, 184, and 52 aredesigned so that aberration can be eliminated without placing the lens181, the optical elements other than the reflecting mirror 52 will beconstructed with one optical block and assembly will be facilitated.

In the imaging device of another embodiment shown in FIG. 39, thereflecting mirror 52, a microshutter 188 operating with an electrostaticforce, made by a micromachine technique, and the image sensor 55 arefabricated on a single silicon substrate 187 by the lithography process.A combination of the silicon substrate 187 with a molded, extendedsurface prism 189 brings about the small-sized imaging unit 180 fordigital cameras, used as the optical apparatus. The microshutter 188 isdesigned to be also usable as a stop.

If the extended surface prism 189 is made by molding plastic, its costcan be reduced. Further, if the extended surface prism 189 isconstructed of energy-curing resin, the durability of the prism becomeshigher than the case of thermoplastic resin, which is favorable.Moreover, the extended surface prism 189 may be constructed of amaterial with the property of absorbing infrared light to bring aboutthe effect of an infrared cutoff filter. Alternatively, an infraredreflecting interference film may be deposited on one surface of theextended surface prism 189 in the optical path to remove infrared light.

A mirror 190 is configured in such a way that the silicon substrate 187is processed into a concave surface, which is coated with aluminum.

The microshutter 188 can be used by improving a shutter such as thatshown, for example, in each of FIGS. 8 and 9 of Japanese PatentPreliminary Publication No. Hei 10-39239.

FIG. 40 shows the microshutter 188, looking at the optical apparatus ofFIG. 39 from above. The microshutter 188 is designed so that potentialdifferences are placed across fixed electrodes 191 and electrodes 193attached to light-blocking plates 192, and thereby the twolight-blocking plates 192 can be opened and closed laterally by anelectrostatic force Fa. Here, the two light-blocking plates. 192 areprovide with triangular notches, one at each middle of adjacent sides ofthe plates, and are shifted to each other in a direction perpendicularto the plane of the figure so that the light-blocking plates 192function as a stop when somewhat opened for photography and act as ashutter when completely closed.

A power supply 196 is such that the sign of a polarity can be changed toa plus or minus. In association with this, the two light-blocking plates192 are to move in opposite directions. The two light-blocking plates192, as shown in FIG. 39, are designed to somewhat overlap whencompletely closed.

The microshutter 188 has the merit that it can be fabricated, togetherwith the reflecting mirror 52 and the solid-state image sensor 55, bythe lithography process. For the microshutter 188, a microshutter suchas that shown, for example, in FIG. 47 of Hei 10-39239 may be used.Alternatively, for the shutter used in the imaging device of thisembodiment, a shutter actuated by a spring, such as that of an ordinaryfilm camera, may be fabricated and placed on the silicon substrate 186.

The imaging device, as shown in FIG. 39, may be constructed to have astop 197 independently. The stop 197 may be an iris diaphragm used forthe lens of the film camera, or as shown In FIG. 41, may be constructedso that a plate with a plurality of holes is slid. Alternatively, afixed stop whose aperture area remains unchanged may be used. Themicroshutter 188 may be actuated as a stop only so that the elementshutter of the solid-state image sensor 55 is used to fulfil itsfunction as a shutter.

Furthermore, the imaging device of the present invention may beconstructed so that at least one of the electrode 54, the mirror 190,the microshutter 188, and the image sensor 55 is fabricated as aseparate part and is placed, together with the remaining parts, on asingle substrate. Also, the imaging device, as shown in FIG. 25, may bedesigned so that the variable focal-length mirror 70 having the variablefocal-length lens in front of a mirror is placed as another modificationexample of the reflecting mirror 52 of the variable optical-propertyelement. In FIG. 25, the variable focal-length mirror 70 has the twistednematic liquid crystal 20 between the transparent electrode 73 and theelectrode 71 which is coated on the surface of the substrate 72 shapedinto a Fresnel lens form. The helical pitch P of the twisted nematicliquid crystal satisfies the following condition:

P<3λ  (11)

When Condition (11) is satisfied, the refractive index of the twistednematic liquid crystal 20 becomes nearly isotropic, irrespective of thedirection of polarization of incident light, and thus a variablefocal-length mirror which does not require the polarizing plate andproduces an image with no blurring is obtained. Also, a low-cost digitalcamera may have practical use even when the pitch P of the twistednematic liquid crystal 20 satisfies the following condition:

P<15λ  (12)

In an embodiment shown in FIG. 42, an optical apparatus 204 is designedso that a reflection type LCD 199, the reflecting mirror 52, and thesolid-state image sensor 55 are provided on a transparent substrate 198and are combined with an extended surface prism 189 which is an opticalblock. The transparent substrate 198 is also provided with a lens 200which is an optical element, a low-pass filter 201, and an IC 203. Thesecomponents constitute a transparent platelike unit 202. The IC 203 is anLSI possessing the function of an IC that drives the reflection type LCD199, the reflecting mirror 52, and the solid-state image sensor 55, orof a CPU for making control and calculation, or a memory. Thesolid-state image sensor 55, the reflecting mirror 52, the reflectiontype LCD 199, and the IC 203 may be fabricated to be independent of oneanother so that they are cemented to the transparent substrate 198.However, If the surface of the transparent substrate 198 is coated witha material such as amorphous silicon, low-temperature polysilicon, orcontinuous crystalline silicon (the Asahi newspaper, Jan. 14, 1998) bythe use of the thin-film transistor technology, this is advantageous forlightweight and compact design and accuracy improvement.

FIG. 43 illustrates the low-pass filter 201 used In the opticalapparatus 204. The low-pass filter 201 is of a pupil division type andconsists of two twisted planar surfaces. The low-pass filter 201 is alsoone of the optical elements. The low-pass filter 201 may be provided onthe extended surface prism 189. In this embodiment, it is desirable thatthe transparent substrate 198 is fabricated by molding glass or resin.

The optical apparatus 204, which can provide both the extended surfaceprism 189 and the transparent platelike unit 202 with the surfaces forreflecting and refracting light, facilitates correction for aberrationand surpasses the imaging unit 180 shown in FIG. 39. Also, the opticalelement such as a lens, for example, like a lens 200 b, may befabricated in such a way that a thin resin film 205 with a curvedsurface is cemented to the surface of a transparent member. Such anapproach is called thin-film lens technology.

In an embodiment shown in FIG. 44, an optical apparatus 207 includes acombination of the transparent platelike unit 202 with the platelikeunit 186. If a lens 208 is provided to be independent of the transparentsubstrate 198, the number of degrees of design freedom for correctionfor aberration will be increased. Although this is advantageous forcorrection for aberration, the lens 208 need not necessarily be used.The transparent platelike unit 202 is provided with a display 209 andthe IC 203, followed by lenses 210 and 211 fabricated through thethin-film lens technology. A lens 212 is constructed integrally with thetransparent substrate 198 by a molding technique when the transparentsubstrate 198 is fabricated. The platelike unit 186 is constructed inthe same way as that shown in FIG. 39.

Each of hatching portions 214 stands for a black light-blocking film foreliminating stray light, which is made by three-layer evaporation ofCr—CrO₂—Cr, black painting, or printing. Also, the hatching portions 214may be provided on the surface, side, and interior of the transparentsubstrate 198 when necessary, but sometimes they are not used.

Although a liquid crystal display which is one example of the display209 can be fabricated on the transparent substrate, for example, ofglass, by the thin-film transistor technology, the solid-state imagesensor 55 can be easily fabricated only on the silicon substrate. Also,a diffraction optical element may be placed on the surface of thetransparent substrate 198, the extended surface prism 189, or theplatelike unit 186.

Since the optical apparatus 207 is designed to separate the substratesfor providing the solid-state image sensor 55 and the display 209, Itscost, in contrast with the case where they are fabricated on the samesubstrate, can be reduced. The material of the transparent substrate 198or the lens 211 of the optical apparatus 207 may be made to have aninfrared absorbing effect so that the role of an infrared cutoff filteris played. Alternatively, an interference film having an infrared cutofffunction may be deposited on the surface of the thin film 53, the lens212, or the transparent substrate 198. Furthermore, the opticalapparatus 207 may be constructed as a display device having an observingfunction, such as that of opera glasses, in an optical system excludingthe solid-state image sensor 55.

In FIG. 45, an optical apparatus 246 includes a combination of aplatelike unit 245 with the extended surface prism 189. The plate-likeunit 245 is constructed with a platelike unit 243 in which thereflecting mirror 52, the mirror 190, and the microshutter 188 arefabricated on a substrate 241 made with a low quality of silicon and aplatelike unit 244 in which the image sensor 55 and the IC 203 arefabricated on a substrate 242 made with a high quality of silicon, boththe platelike units 243 and 244 being placed on a single substrate 240.The image sensor 55 and the IC 203 can be easily fabricated only on ahigh-quality silicon substrate, but the mirror 190, the microshutter188, and the reflecting mirror 52 are fabricated even on a low-qualitysilicon substrate.

According to the optical apparatus 246 of this embodiment, the platelikeunits 243 and 244 which are optical units are constructed with separatesubstrates of different qualities, and hence the amount of use of a highquality of silicon can be reduced accordingly. This is advantageous forcost.

The extended surface prism 189 is provided with legs 247 and 248, whichare capable of adjusting an optical length between respective surfacesto a desired design value when constructed integrally with the platelikeunit 245.

In FIG. 46, the optical apparatus Is such that an imaging device fordigital cameras is constructed by combining the extended surface 189with the platelike unit 243 and the solid-state image sensor 55.According to the optical apparatus, the image sensor 55 is separatedfrom the substrate 241 made with a low quality of silicon, and thus acommercial CCD can be used as the image sensor 55. This reduces cost.

It is favorable that the optical apparatus of the embodiment is providedwith another liquid crystal display, not shown, and is used as a finderfor digital cameras.

In this embodiment, the reflecting mirror 52, the mirror 190, and themicroshutter 188, instead of being placed on a single substrate, asshown in FIG. 47, may be placed to be independent of one another aroundthe extended surface prism 189. Since in this case the optical parts ofthe reflecting mirror 52, the mirror 190, and the microshutter 188 canbe separately made, these parts can also be used as parts of otherproducts. Even when the yield (the ratio of good to bad parts onfabrication) of the optical parts is low, only good parts can be chosento fabricate products, and thus the yield on products is improved,compared with the case where the optical parts are fabricated on asingle substrate.

As shown in FIG. 46, a liquid crystal shutter 249 which is one ofvariable transmittance elements may be placed in front of thesolid-state image sensor 55. In this case, the microshutter 188 may beactuated as a stop or a shutter in accordance with the liquid crystalshutter 249. Alternatively, the shutter operation may be performed bythe functions of the liquid crystal shutter 249 and the element shutterof the image sensor 55, excluding the microshutter 188. The liquidcrystal shutter 249 has no mechanical moving parts, and therefore if themicroshutter 188 is eliminated, a mechanical structure can besimplified.

In FIG. 48, an optical apparatus 217 is designed to have a legged lens216 which is an example of an optical moving element. Moreover, theoptical apparatus 217 is constructed so that the transparent substrate198 is combined with the solid-state image sensor 55 and the extendedsurface prism 189. The legged lens 216 is provided with legs 219,beneath a lens 218, fabricated by a micromachine technique set forth in“Micromachined free-space integrated micro-optics”, by M. C. Wu, L.-Y.Lin, S.-S. Lee, and K. S. J. Pister, Sensors and Actuators A 50, pp.127-134, 1995.

The legs 219 are connected to electrodes 219 b (FIG. 49) slid by anelectrostatic force, corresponding to an electrode 193 b shown in FIG.69 to be depicted later, so that, in FIG. 49, the electrodes 219 b areslid and thereby an angle θ is changed. In accordance with the change ofthe angle θ, intersections P₁ and P₂ with the legs 219 are moved alongthe surface of the transparent substrate 198. In this way, the leggedlens 216 is such that when the angle θ made with each leg 219 is changedand a distance L between the lens 218 and the transparent substrate 198is varied, the focusing adjustment can be made. Between the transparentsubstrate 198 and the extended surface prism 189 shown in FIG. 48, aslight air space is provided so that the light 60 from the object istotally reflected at a point A.

FIG. 49 shows a modification example of the foregoing embodiment whichis an imaging device with a simple structure combining the legged lens216 with the transparent substrate 198 and the image sensor 55. Also,reference numeral 219 c denotes fixed electrodes.

FIG. 50 shows another embodiment of the present invention. Thereflecting mirror 52 is constructed so that when a voltage is appliedacross the thin film 53 and a plurality of electrodes 54, the thin film53 is deformed by an electrostatic force and its surface profile ischanged, like a membrane mirror set froth, for example, in “Hand-book ofMicrolithography, Micromachining, and Microfabrication”, by P.Rai-Choudhury, Vol. 2, Micromachining and Microfabrication, p. 495, FIG.8.58, SPIE PRESS, or “Flexible mirror micromachined in silicon”, by GlebVdovin and P. M. Sarro, Applied Optics, Vol. 34, No. 16, pp. 2968-2972,1995. In this way, the imaging device is capable of making compensationsfor deformations and variations of refractive indices of the opticalelements 181, 182, 183, 184, and 185, or the expansion, contraction, anddeformations of frames 301 and 302 caused by temperature and humiditychanges, or a reduction in imaging performance caused by the opticalelements; corrections for assembly errors of parts, such as the frames,and the optical elements; and shake prevention, focusing adjustment, andcorrection for aberration caused by the focusing adjustment. In theimaging device of this embodiment, the light 60 from the object isrefracted by the exit and entrance surfaces of the prism 184 andreflected by the reflecting mirror 52. The light is then reflected bythe reflecting surface of the mirror 185, and after being refracted bythe lens 183, falls on the solid-state image sensor 55.

In the optical apparatus of FIG. 50, the surface profile of thereflecting mirror 52 is controlled by actuating the variable resistor 59with a signal from an arithmetical unit 304 so that imaging performanceis optimized. Signals delivered from a temperature sensor 303, ahumidity sensor 305, a range sensor 306, and a shake sensor 311 enterthe arithmetical unit 304, and thereby voltages applied to theelectrodes 54 are determined at the arithmetical unit 304 to compensatefor the reduction of imaging performance. The value of the variableresistor 59 is thus changed. In this way, the thin film 53, which isdeformed by different electrostatic forces, assumes various shapesincluding an aspherical surface in accordance with the situation. Theshape of the thin film 53 is depicted to be concave in the figure, butif the sign of the voltage is changed every electrode, a convex andconcave surface can be configured. This is favorable because variouschanges of situation can be accommodated. Also, the range sensor 306 maybe eliminated, and in this case, when the shape of the reflecting mirror52 is somewhat changed and is determined so that the high-frequencycomponent of the MTF of an image signal from the image sensor 55 ispractically maximized, the focusing adjustment can be made. In theoptical apparatus of FIG. 50, the reflecting mirror 52 can also befabricated by the silicon lithography process. If the material of thethin film 53 is synthetic resin such as polyimide, a considerabledeformation can be caused even at a low voltage. In this embodiment, thereflecting mirror 52 is constructed integrally with the image sensor,and this is advantageous for compactness and cost reduction.

A description will be further given of the reflecting mirror 52. FIG. 51shows a reflecting mirror 52B which is another example of the reflectingmirror 52. The reflecting mirror 52B is a variable mirror in which apiezoelectric element 310 is sandwiched between the thin film 53 and theelectrodes 54, and a voltage applied to the piezoelectric element 310 ischanged every electrode 54 so that different expansion and contractionare caused to various portions of the piezoelectric element 310 tochange the shape of the thin film 53. It is desirable that theconfiguration of the electrodes 54 is properly chosen, for example, tobe concentric, as illustrated in FIG. 52, or divided-rectangular, as inFIG. 53. Amplifiers 312 are controlled by the calculation of thearithmetical unit 304 and voltages applied to the electrodes 54 arevaried so that the thin film 53 is deformed by the shake sensor 311 inorder to compensate for a camera shake caused by hand holding of thedigital camera in photography.

In this case, the signals from the temperature sensor 303, the humiditysensor 305, and the range sensor 306 are delivered at the same time, thefocusing adjustment and compensation for temperature and humidity aremade. Since the stress of the piezoelectric element 310 is imposed onthe thin film 53, it is desirable that the thin film 53 is made to havesome extent of thickness so that its strength is held. Also, referencenumeral 313 represents a base.

Alternatively, the voltages applied to the electrodes 54 may be slightlychanged during photography to shift the position of an image, therebycausing a low-pass filter effect to the reflecting mirror 52B forelimination of moire.

FIG. 54 shows a reflecting mirror 52C which is another example of thereflecting mirror 53. The piezoelectric element 310 shown in FIG. 51 isreplaced by piezoelectric elements 310A and 310B made with materialspossessing piezoelectric characteristics in opposite directions. If thepiezoelectric elements 310A and 310B are constructed of ferroelectriccrystals, the crystal axes of the piezoelectric elements 310A and 310Bare reversed in direction. By doing so, when the voltage is applied, thepiezoelectric elements 310A and 310B expand and contract in oppositedirections, and hence the force of deforming the thin film 53 becomesstronger than the case of the reflecting mirror 52B. Consequently, thesurface profile of the mirror can be considerably changed. In addition,the thickness of each of the piezoelectric elements 310, 310A, and 310Bis made uneven, and thereby the shape of the thin film 53 can beproperly deformed.

The piezoelectric elements 310, 310A, and 310B include, for example, thefollowing: piezoelectric substances such as barium titanate, Rochellesalt, quartz crystal, tourmaline, KDP, ADP, and lithium niobate;polycrystals or crystals of the piezoelectric substances; piezoelectricceramics such as solid solutions of PbZrO₃ and PbTiO₃; organicpiezoelectric substances such as PVDF; and other ferroelectrics. Inparticular, the organic piezoelectric substance is favorable because ithas a small value of Young's modulus and brings about a considerabledeformation at a low voltage.

FIG. 55 shows a reflecting mirror 52D which is another example of thevariable mirror. Voltages are applied to the piezoelectric element 310,across the thin film 53 and an electrode 325, through drive circuits326, and thus a mirror 331 is deformed. Since the electrodes 54 are alsoprovided, the mirror 331 is deformed even by an electrostatic force. Thereflecting mirror 52D, in contrast with the reflecting mirrors 52, 52B,and 52C, can provide various deformation patterns and is quick inresponse.

FIG. 56 shows a variable mirror 52E utilizing an electromagnetic forcewhich is still another embodiment of the present invention. The variablemirror 52E can be used instead of the variable mirror 52. A plurality ofcoils 362 are arranged above a permanent magnet 361 and are constructedintegrally with a substrate 363 of the mirror. The substrate 363 is madewith silicon nitride or polyimide. A reflecting film 364 consisting of ametal coating, for example, an Al coating, is deposited on the surfaceof the substrate 363 to construct a reflecting mirror. When properelectric currents flow through the coils 362 from the drive circuits365, the coils 362 are repelled or attracted by the electromagneticforce with the permanent magnet 361, and the substrate 363 and thereflecting film 364 can be deformed. In response to changes of theoptical system obtained by signals from the sensors 303, 305, 306, and311, the signals are transmitted from the arithmetical unit 304 to thedrive circuits 365, and the substrate 363 and the reflecting film 364are deformed. Different currents can also flow through the coils 362.The plurality of coils 362 need not necessarily be used, that is, asingle coil may be used. Furthermore, the permanent magnet 361 may beprovided on the substrate 363, and the coils 362 may be provided on theside of a substrate 368. It is desirable that the coils 362 arefabricated by the lithography process. A ferromagnetic core (iron core)may be encased in each of the coils 362.

FIG. 57 shows a variable mirror 52F which is another example of thevariable mirror utilizing the electromagnetic force. A plurality ofcoils 369 are arranged on the substrate 368 opposite to a thin-film coil367 provided on the back surface of the substrate 363. A plurality ofvariable resistors 370 a are energized and thereby the electromagneticforce exerted between the thin-film coil 367 and the coils 369 is variedto deform the substrate 363, so that this system can be operated as avariable mirror. By reversing the operation of a switch 371, thedirection of the currents flowing through the coils is changed, and thewhole of the substrate 363 and the thin film 364 can be deformed to haveeither a concave or convex surface. Reference numeral 370 denotes avariable resistor. The configuration of the coil 367, as shown in FIG.58, is changed so that a coil density varies with place, and thereby adesired deformation can be brought to the substrate 363 and the thinfilm 364. Instead of the plurality of coils 369, as shown in FIG. 59, asingle coil 369 a may be used. A ferromagnetic core (iron core) may beencased in the coil 369 a.

FIG. 60 shows a reflecting mirror 52G which is another example of thevariable mirror utilizing the electromagnetic force. The reflecting film364 is deposited on a mirror substrate 372 which is made with aferromagnetic, for example, iron. The reflecting mirror 52G, in contrastwith the mirror of FIG. 57, dispenses with the coil 367, so that itsfabrication is easy and cost reduction can be achieved accordingly. Byvarying the currents flowing through the coils 369, the substrate 372can be arbitrarily deformed.

FIG. 61 shows one configuration of the coils 369, looking at from above.FIG. 62 shows another configuration of the coils 369, looking at fromabove.

The configuration of the coils shown in each of FIGS. 61 and 62 isapplicable to the coils 362 of the reflecting mirror 52E and the coils369 of the reflecting mirror 52F.

FIG. 63 shows the configuration of permanent magnets which can be usedin the reflecting mirror 52E, together with an array of coils in FIG.62. A plurality of bar magnets 373 are radially arranged. The barmagnets 373, in contrast with the permanent magnet 361, are capable ofproviding a delicate deformation to the substrate 363 and the thin film364. Each of the variable mirrors 52E, 52F, and 52G using theelectromagnetic force has the merit that it can be drived at a lowvoltage, compared with the variable mirror using the electrostaticforce.

In some embodiments of the present invention, the extended surface prism189 is used, but instead of this, as shown in FIG. 64, a reflectingmirror 401 having an extended surface may be used. The reflectingsurface of the reflecting mirror 401 is configured as the extendedsurface. The reflecting mirror 401, in contrast with the extendedsurface prism, has the merit that its weight is light because of ahollow mirror. This figure is cited as an example of the bar-codescanner of an electronic imaging device.

In the present invention, as show in FIG. 65, at least two variablemirrors can also be used to construct the optical system. In doing so,the shake prevention and the focusing adjustment can be made by separatevariable mirrors, and this increases the number of degrees of freedom ofoptical design. Alternatively, at least two variable mirrors can be usedin one optical system to perform the zooming operation, focusingadjustment, and shake prevention of the optical system. This figure iscited as an example of a digital camera.

As is true of any optical apparatus in the present invention, it isdesirable that the variable mirror is placed close to the stop of theoptical system. It is for this reason that since a ray height is low inthe proximity of the stop, the size of the variable mirror can bereduced, and a response speed, as well as cost and weight, isunsurpassed.

In an embodiment shown in FIG. 66, an optical apparatus is constructedas a finder for digital cameras which is an example of an observingdevice. The optical apparatus of the present invention is provided witha legged mirror 216B in which the lens 218 of the legged lens 216 shownin FIGS. 48 and 49 is replaced by a mirror 218B. Besides the leggedmirror 216B, the optical apparatus has the platelike unit 186 includingthe transparent substrate 198 and a lens 411 and the extended surfaceprism 189. The optical apparatus of the present invention is designed sothat the legs 219 are slid to change the distance L between the mirror218B and the transparent substrate 198 and thereby the diopteradjustment can be made. The legged lens 216 shown in FIGS. 48 and 49 isused as an example of a moving lens which is one of the moving opticalelements. As another example of the moving lens, an electrostatic lensis cited.

FIG. 67 shows this electrostatic lens. An electrostatic lens 420 isprovided with the lens 218, electrodes 421 and 422, and a damper 423.The electrostatic lens 420 is designed so that a voltage is appliedacross the electrodes 421 and 422, and thereby a distance between thelens 218 and the transparent substrate 198 is changed by anelectrostatic force to perform the focusing and zooming operations. Thedamper 423 is adapted to hold the lens 218 and absorb a shockexperienced when the lens 218 is moved.

In an embodiment shown in FIG. 68, an optical apparatus 428 isconstructed with the reflecting mirror 52 which is one of the variableoptical-property elements, a moving mirror 426 which is one of themoving optical elements, and a self-running lens 427 which is an exampleof the moving lens of one of the moving optical elements. In addition,the optical apparatus 428 is provided with the silicon substrate 187 andthe extended surface prism 189.

The optical apparatus 428 is designed so that the focal length of thereflecting mirror 52 and the positions of the self-running lens 427 anda mirror 425 are changed, and thereby the zooming and focusingoperations can be performed.

The extended surface prism 189 used in this embodiment may beconstructed of a material absorbing infrared light to have an infraredcutoff effect. The lens 218 shown in FIG. 67 may be replaced with themirror 425 as the moving mirror 426 so that the mirror 426 is used asthe moving optical element in the above embodiment.

The self-running lens 427, as depicted in FIG. 69, has electrodes 193 aand 193 b and the lens 218 fixed to the electrode 193 b so that apotential difference are placed across the two comb-shaped electrodes193 a and 193 b and the lens 218 can be moved in the direction of anarrow by the electrostatic force.

Recently, compactness of digital cameras has been required, and inparticular, card type thin digital cameras are excellent and convenientfor carrying. However, in an imaging device combining a conventionaloptical system and electric system, there is a limit to compactness.

Thus, the present invention is made so that an Imaging device and anoptical apparatus used in the card type thin digital cameras can beprovided.

An optical apparatus shown in FIG. 70 constructs a digital camera 432which uses an imaging unit 431 combining an extended surface prism 430which is one of the optical blocks, on a platelike unit. The digitalcameras 432 is also provided with the display 209 such as a liquidcrystal display. The digital camera 432 is designed so that the imagingunit 431 is capable of imaging an object situated in a direction along athickness Ta of the digital camera 432.

In FIGS. 71 and 72, the extended surface prism 430 is such that thelight 60 from the object is reflected by a reflecting surface Ra, andafter changing its direction in the x-y plane and toward the reflectingmirror 52 and being reflected thereby, is reflected by a reflectingsurface Rb to enter the solid-state image sensor 55. In this way, whenthe extended surface prism 430 is constructed so that the light 60incident on the extended surface prism 430 has a helical relationshipwith a ray of light m emerging from the extended surface prism 430 andentering the solid-state Image sensor 55, the thickness of the digitalcamera 432 can be reduced to the same extent as a width W of the imagesensor 55.

Instead of the extended surface prism 430, the optical element such as alens or prism which is commonly used, or the extended surface prism suchas the optical block 189 shown in FIG. 39 may be used to construct anoptical system so that the ray of light m incident on the image sensor55 has the helical relationship with the incident light 60 from theobject. An infrared cutoff interference film 433 may also be placed inthe optical path of the extended surface prism 430.

An optical apparatus shown in FIG. 73 is another example of the digitalcamera which is different from that of FIG. 70, and uses the imagingunit 180 for small-sized digital cameras shown in FIG. 39 to construct adigital camera 434. The digital camera 434 of this embodiment isdesigned so that the imaging device 180 for small-sized digital camerasis capable of imaging an object situated in a direction perpendicular tothe direction of the thickness Ta of the digital camera 434. Accordingto this embodiment, the imaging unit 180 for small-sized digital camerasis placed so that the incident light from the object makes a right anglewith the direction of the thickness Ta of the digital camera 434, andhence the thickness of the digital camera 434 can be reduced.

Also, in the imaging device of the digital camera, besides the imagingunit shown in each of FIGS. 70 and 73, either the platelike unit orapparatus of the present invention can be used. The plate-like unit orapparatus may be used in the optical system or Imaging device other thanthat of the digital camera, for example, of the PDA.

In recent years, electronic imaging devices for electronic cameras andvideo cameras have increased. In most cases, each of these devices, asshown in FIG. 74, is constructed with a combination of a solid-stateimage sensor 501 and a lens system 502. Since, however, such a device,which is complicated in structure, has a large number of parts and istroublesome to set up, there are limits to compactness and costreduction.

Thus, the present invention is made so that an electronic imaging devicewhich is small in size and low in cost can also be provided. The opticalapparatus of the present invention for achieving this purpose isdesigned so that at least one image sensor and one optical element areplaced on the surface of a single transparent substrate to have animaging function by themselves or by adding other parts.

In an imaging device shown in FIG. 75, extended surfaces 504 and 506 anda diffraction optical element (hereinafter referred to as DOE) 505 areconfigured on both surfaces of a single transparent substrate 503 madewith glass, crystal, or plastic, and a solid-state image sensor 501 isalso fabricated on the surface thereof by a silicon thin-film technique.This is called a platelike imaging unit 507. The extended surface isused for either a refracting or reflecting function. In the embodiment,the light 60 from the object is refracted by the extended surface 504,and after deflection and reflection by the off-axis type DOE 505, isreflected by the extended surface 506 to form an image on thesolid-state image sensor 501. Since the extended surfaces 504 and 506and the ODE 505 are corrected for aberration, a good image formed to thesame extent as in an ordinary lens system enters the solid-state imagesensor 501. The extended surfaces 504 and 506 may be configured by amolding technique and the DOE 505 may be fabricated by a molding orlithography technique, together with the solid-state image sensor 501.The solid-state image sensor 501 may be fabricated directly on thetransparent substrate 503 by the lithography technique. In case wherethis is difficult, however, the solid-state image sensor 501 may beseparately prefabricated before it is constructed integrally with thetransparent substrate 503. Alternatively, although not shown in thefigure, parts such as lenses may be additionally placed outside theplatelike imaging unit 507 so that these parts and the platelike imagingunit 507 have an imaging function. Also, the DOE 505 may be placed onthe surface of the transparent substrate 198, the extended surface prism189, or the platelike unit 186.

In FIG. 76, an optical apparatus is a unit for personal digitalassistants in which the imaging unit 507 is fabricated, together with aTFT liquid crystal display 508, ICs 509 of peripheral circuitry, and amicroprocessor 510, on the transparent substrate 503. The imaging unit507 may also be fabricated, together with an IC (LSI) having thefunctions of a memory and a telephone. A finder 511 of the electronicimaging device is also provided on the transparent substrate 503. Thefinder 511 may have a simple structure such that only a field frame isplaced on the transparent substrate 503, or as shown in FIG. 77, may beprovided with a negative lens 512 and a positive lens 513 in bothsurfaces of the transparent substrate 503 to construct a Galileantelescope type finder. Alternatively, at least one of the negative lens512 and the positive lens 513 may be placed outside the transparentsubstrate 503 to construct a finder, together with the remaining lens onthe transparent substrate 503.

In FIG. 78, an optical apparatus is a platelike imaging unit in whichthe focusing adjustment is possible. Where the focusing adjustment ismade by a platelike imaging unit 514, it is impossible to mechanicallyshift the positions of the DOE 505 and the extended surface 506 shown inFIG. 75. Thus, the platelike imaging unit 514 of this embodiment uses anoptical element 515 in which the focal length is variable. FIG. 79 showsan example of the optical element 515. It is a variable focal-length DOE517 using a macromolecular dispersed liquid crystal 516. At least onesurface of a transparent substrate 518 is provided with a groove with awidth nearly equal to the wavelength of light. When a voltage is appliedto a transparent electrode 519, the orientation of liquid crystalmolecules 520, as shown in FIG. 80, becomes uniform, and therefore therefractive index of the macromolecular dispersed liquid crystal 516 islowered. On the other hand, when no voltage is applied, the liquidcrystal molecules 520 are oriented at random, and thus the refractiveindex of the macromolecular dispersed liquid crystal 516 is raised. Inthis way, the variable focal-length DOE 517 is capable of changing thefocal length by applying or removing the voltage. When the weight ratioof the liquid crystal molecules 520 to the macromolecular dispersedliquid crystal 516 is increased over some extent (for example, more than25%), the macromolecular dispersed liquid crystal 516 approaches a solidphase, and thus a substrate need not be provided on the right side ofthe macromolecular dispersed liquid crystal 516. Moreover, as shown inFIG. 81, the right-side surface of the macromolecular dispersed liquidcrystal 516 and the left-side surface of the transparent substrate 518may be configured as curved surfaces 521 a and 521 b, respectively, tohave a lens function and correct aberration. In each of FIGS. 79 and 81,the right-side surface of the transparent substrate 518 may beconfigured not as an DOE surface, but as a fresnel surface. In thiscase, the DOE 517 acts as a variable focal-length Fresnel lens. Inaddition, as shown in FIG. 82, the right-side surface of the transparentsubstrate 518 may also be configured as a curved surface such as that ofan ordinary lens. Each of the transparent substrates 503 and 518 may bedesigned to have the effect of an infrared cutoff filter.

In FIG. 83, an optical apparatus is a platelike imaging unit using areflection type variable focal-length Fresnel mirror 522. The variablefocal-length Fresnel mirror 522, as shown in FIG. 84, is provided with areflecting surface 523 so that the refracting power of a Fresnel surface526 is changed by varying a voltage through a switch 524 or a variableresistor 525, and hence behaves as a variable focal-length Fresnelmirror. Instead of the Fresnel surface 526, the DOE may be used.

The variable focal-length DOE 517 and the fresnel mirror 522 of thisembodiment may be used not only in the platelike imaging unit 507, butalso, as shown in FIG. 85, in an ordinary imaging device, or a variablefocal-length lens system for optical disks with different thicknesses,an electronic endoscope, a TV camera, or a film camera. It is favorablethat a tolan-base liquid crystal, for example, Dai Nippon Ink DON-605:N-1 (Jap. Chem. pp. 14-18, February, 1997) is used. This is because theliquid crystal is good in optical isotropy (Δn =0.283, where Δn standsfor an optical isotropy, which is a difference in length between themajor axes of index ellipsoids), low in viscosity, and is capable ofchanging the focal length with high speed.

Also it is advantageous for fabrication and cost that the sizes of thevariable optical-property element, the moving optical element, theshutter, the stop, the display element, and the imaging element whichare used in the present invention are less than 7 cm. The sizes of lessthan 3 cm are more advantageous.

What is claimed is:
 1. An optical system comprising: a reflection-typevariable optical-property element, wherein the reflection-type variableoptical-property element has a variable light-deflecting function, saidreflection-type variable optical-property element compensates, bychanging a light-deflecting function thereof, for a change of an imagingstate in the optical system that is caused by at least one of a changeof an imaging magnification and a change of an imaging state in theoptical system that is caused by a change of an object.
 2. An opticalsystem comprising: a variable optical-property element excluding avariable apex-angle prism, wherein the variable optical-property elementhas a variable light-deflecting function, said variable-optical propertyelement works, by changing a light-deflecting function thereof, for atleast one of compensating for a temperature change, compensating for ahumidity change, compensating for a fabrication error, compensating foran assembly error, reducing moire, and improving resolving power.
 3. Anoptical system according claim 1, wherein the reflection-type variableoptical-property element has a reflecting surface, a reflecting regionwhich has different lengths along two directions perpendicular to oneanother, and the reflection-type variable optical-property element isarranged so that incident light and reflected light travel along alongitudinal direction thereof.
 4. An optical system comprising: areflection-type variable optical-property element, wherein thereflection-type variable optical-property element has a variablelight-deflecting function, said reflection-type variableoptical-property element compensates, by changing a light-deflectingfunction thereof, for a deviation from a designed value.
 5. An opticalsystem comprising: a reflection-type variable optical-property element,wherein the reflection-type variable optical-property element has avariable light-deflecting function, said reflection-type variableoptical-property element works, by changing a light-deflecting functionthereof, for at least one of compensating for a shake, compensating fora temperature change, compensating for a humidity change, compensatingfor a fabrication error, compensating for an assembly error, reducingmoire, and improving resolving power.
 6. An optical system comprising: areflection-type variable optical-property element, wherein thereflection-type variable optical-property element has a variablelight-deflecting function, said reflection-type variableoptical-property compensates, by changing a light-deflecting functionthereof, for a defocus or an aberration change.
 7. An optical systemcomprising: a variable optical-property element excluding a variableapex-angle prism; wherein the variable optical-property element has avariable light-deflecting function, said variable optical-propertyelement compensates, by changing a light-deflecting function thereof,for a deviation from a designed value.
 8. An optical system comprising:a variable optical-property element excluding a variable apex-angleprism; wherein the variable optical-property element has a variablelight-deflecting function, said variable optical-property elementcompensates, by changing a light-deflecting function thereof, for adefocus or an aberration change.
 9. An optical system comprising: avariable optical-property element driven by an electrostatic force or anelectromagnetic force, wherein the variable optical-property element hasa variable light-deflecting function, said variable optical-propertyelement compensates, by changing a light-deflecting function thereof,for a change of an imaging state in the optical system that is caused bya change of an imaging magnification or for a change of an imaging statein the optical system that is caused by a change of an object.
 10. Anoptical system comprising: a variable optical-property element that hasa deformable surface, wherein the variable optical-property element hasa variable light-deflecting function, said variable optical-propertyelement compensates, by changing a light-deflecting function thereof,for a deviation from a designed value.
 11. An optical system comprising:a variable optical-property element that has a deformable surface,wherein the variable optical-property element has a variablelight-deflecting function, said variable optical-property element works,by changing a light-deflecting function thereof, for at least one ofcompensating for a shake, compensating for a temperature change,compensating for a humidity change, compensating for a fabricationerror, compensating for an assembly error, reducing moire, and improvingresolving power.
 12. An optical system comprising: a variableoptical-property element that has a deformable surface, wherein thevariable optical-property element is constructed to have a variablelight-deflecting function, and compensates, by changing alight-deflecting function thereof, for a defocus or an aberrationchange.
 13. An optical system comprising: a variable focus lens, whereinthe variable focus lens has a variable light-deflecting function, saidvariable focus lens works, by changing a light-deflecting functionthereof, for change of an imaging state or for compensating for animaging state.
 14. An optical system comprising: a variable focus lens,wherein the variable focus lens has a variable light-deflectingfunction, said variable focus lens compensates, by changing alight-deflecting function thereof, for a deviation from a designedvalue.
 15. An optical system comprising: a variable focus lens, whereinthe variable focus lens has a variable light-deflecting function, saidvariable focus lens works, by changing a light-deflecting functionthereof, for at least one of compensating for a shake, compensating fora temperature change, compensating for a humidity change, compensatingfor a fabrication error, compensating for an assembly error, reducingmoire, and improving resolving power.
 16. An optical system comprising:a variable focus lens, wherein the variable focus lens has a variablelight-deflecting function, said variable focus lens compensates, bychanging a light-deflecting function thereof, for a defocus or anaberration change.
 17. An optical system comprising: an optical element;and an actuator connected with the optical element, wherein the actuatoris driven by an electrostatic force, said actuator works, by moving theoptical element, for change of an imaging state or for compensating foran imaging state.
 18. An optical system comprising: an optical element;and an actuator connected with the optical element, wherein the actuatoris driven by an electrostatic force, said actuator compensates, bymoving the optical element, for a deviation from a designed value. 19.An optical system comprising: an optical element; and an actuatorconnected with the optical element, wherein the actuator is driven by anelectrostatic force, said actuator works, by moving the optical element,for at least one of compensating for a shake, compensating for atemperature change, compensating for a humidity change, compensating fora fabrication error, compensating for an assembly error, reducing moire,and improving resolving power.